Which set point are they talking about?

[Radian]

Looking at the Glow-worm technical guide that applies to my condensing boiler, I'm not sure which set point they're referring to in the following flowchart:

 

• "Does boiler modulate before desired set point is reached?"
• "Does boiler go off before desired set point is reached?"

 

Which set point? The demand thermostat or the boiler flow temperature?

Because the boiler can have load/weather compensation the boiler flow temperature might be variable so how would you know what the setpoint was?

I'm guessing it must mean the external heating controls.

 

Incidentally, I'm poking about in this area to make sure that I have the optimum setting for my circulating pump head.

[JohnMo]

Not got the same boiler, but have found on mine, the following.

 

On the controller there is a user menu and an installer menu.  In the installer menu under the info tab, can see what the set point is for the boiler. Ours is running WC, and when I looked last the set point was 30.  The heating pump runs all the time in WC, when the return temp has dropped a couple of degrees below set point, the boiler fires up. On mine I can set what is called the gradient, this is how quickly the boiler gets up to temp, I have set this as low as I can, so the boiler run time is high.  Once the boiler has got to the set point temperature on the return water or if the max supply temp has been reached the boiler switches off.  My max is set to 40, so boiler either goes to 40 or a return temp of 30 which ever occurs first.

[SimonD]

16 hours ago, Radian said:

Which set point? The demand thermostat or the boiler flow temperature?

 

In this instance I believe that the flowchart is referring to the room thermostat set point rather than the flow temperature set point. Ideally you want to see the programmer/boiler modulating before this set point is reached. (Interestingly on my Honeywell Evohome setup it tells me the percentage modulation compared to the boiler flow set point, which as you say will vary according to how close the room is to its set point and weather conditions)

 

It seems, however, that the flow chart is a troubleshooting one that looks at diagnosing problems with modulating or cycling of the boiler due to flow rate issues within the heating system? I've seen this recently where low flow rate causes a too high flow/return temp differential (e.g. more than 38C and thus eventually throws a fault at the boiler), or that flow temp rises too fast so the boiler has to switch off (flow temp rises above the flow temp set point and too quickly), again due to low flow rates. With the new building regs I reckon there's going to be far more head scratching going on with Delta T/Flow Rates/Modulation/Cycling - in the real world it's turning out to be a time consuming process to get right! I'm finding quite a few issues setting all this up with new boiler installations on existing heating systems.

 

Does your boiler have a flow rate sensor and a way you can access this information? Then put in a phone call to Glow worm customer technical support and see if they can give you specific flow rate figures to work by (Sometimes they don't like giving out too much info mind you). Alternatively, there's a straightforward calc given by Grundfos: https://www.grundfos.com/sg/learn/research-and-insights/calculation-of-flow. Or there's the CIBSE Domestic Heating Design Guide that has a more detailed section on flow rates: https://www.cibse.org/knowledge-research/knowledge-portal/domestic-heating-design-guide-2021

Edited December 26, 2022 by SimonD

[Radian]

7 hours ago, SimonD said:

It seems, however, that the flow chart is a troubleshooting one that looks at diagnosing problems with modulating or cycling of the boiler due to flow rate issues within the heating system?

 

Yes, as I don't have a flow meter I'm only able to use approximations like the grundfos link provides. Having very little confidence with that I was looking at the modulating behaviour of the boiler.

 

7 hours ago, SimonD said:

With the new building regs I reckon there's going to be far more head scratching going on with Delta T/Flow Rates/Modulation/Cycling - in the real world it's turning out to be a time consuming process to get right! I'm finding quite a few issues setting all this up with new boiler installations on existing heating systems.

 

Now you're talking about something very dear to my heart! I'm highly intrigued by the recent changes to Part L covering the replacement of boilers and the requirement for radiators to be sized for operation at 55^oC This is very eye-catching for people like me with a 14 year old boiler expecting it to be pushing up the daisies any day now. I've read interesting discussions in social charity circles about the impact this change in legislation will have on home owners. The stats on boiler replacement show that many are carried out in emergency situations - AKA distress purchases where loss of heating and hot water are serious events requiring rapid solutions that need to place a minimal cost burden on low-income families.

 

Then along comes the heating engineer obliged to meet Part L in whatever way they can. On the menu will potentially be expensive high efficiency radiators to replace ones that only worked adequately on 75^oC flow and expensive heating controls to tease out the last few drops of efficiency (or in the case of heat-only or regular boilers with HW cylinders, external controls to provide separate flow temps for CH and DHW (e.g. another ~£500 to get this functionality out of my current boiler)). I'd love to know your experience of this?

[SteamyTea]

I have just been to the Screwfix website, searched for central heating controllers.

I can see why there is a problem.  There is 104 different types.

 

https://www.screwfix.com/c/heating-plumbing/central-heating-controls/cat831042#category=cat831042&page_size=100&page_start=0

[Radian]

20 minutes ago, SteamyTea said:

I have just been to the Screwfix website, searched for central heating controllers.

I can see why there is a problem.  There is 104 different types.

 

https://www.screwfix.com/c/heating-plumbing/central-heating-controls/cat831042#category=cat831042&page_size=100&page_start=0

 

It's an awful mess. There are numerous 'simple' types, some smart, some not so much. But by 'simple' I mean bang-bang relay on/off to place a demand or not. Then there are the more nuanced controls that communicate with the boiler to adjust flow rate/pump speed for weather/load compensation etc. These rely on a common digital protocol - opentherm being the chief one. But not all manufacturers use this - Glow-worm have their own incompatible and undocumented standard.

 

This is where I'm struggling a bit at the moment. The pain of the Glow-worm ebus control system is that you need a 'smart' wiring center (~£80) and a separate 'smart' control user interface (~£300) for these disparate units talk ebus to the boiler. Without this lot, the boiler has only one flow temperature to provide both heating and hot water. If you want to set the radiator flow to 55^oC, this isn't enough for HW.

 

I've been looking at a drop-in replacement for my boiler and because the water pipes are at the top, exhaust at the back and gas & condensate drain are at the bottom, realistically I'm stuck with another Glow-worm.

[SteamyTea]

1 minute ago, Radian said:

These rely on a common digital protocol - opentherm being the chief one.

And now Matter is coming along, so another one to play with.

1 minute ago, Radian said:

It's an awful mess.

Yes Captain Manwaring, an awful mess.

Like people in a carpark.  They get there by adhering to a few simple and well understood rules, get out their vehicles and, for some unknown reason, make up their own protocols about the best way to move about.

[Radian]

I say its a mess because the motive for ensuring heating systems are ready for heat pumps is all fine and sensible. But in Europe, manufacturers are legally obliged to provide equipment that is compatible with a single standard (opentherm) in fact Glow-worm (probably begrudgingly) make an adapter that converts their proprietary ebus to the opentherm protocol just so they can service that market. But they seem to go out of their way to keep these out of the UK market because it would allow people to jail-break their ecosystem and benefit from the open-market for less expensive controls.

 

I find it ironic that the motive for the recent changes to Part L are to make systems ASHP ready - with one big problem being the lack of DHW cylinders in homes given the widespread adoption of combi boilers. But people like me with heat-only or system boilers that actually do have cylinders can't easily operate them with independent flow temperatures because the boilers don't have independent demand inputs. This level of control apparently being somewhat exotic, requiring expensive external control options.

[SimonD]

On 26/12/2022 at 22:31, Radian said:

I'd love to know your experience of this?

 

My experience is so far is mixed. With the new Part L we're technically only required to design to 55C flow temps where there is a new heating system installation. When it comes to replacing a boiler, it's about ensuring that the new one doesn't perform any worse than the one you're replacing and then that controls are installed that provide either weather/load compensation, or automisation/optomisation, or flue gas heat recovery. There is also a requirement that if you install a new boiler you should also install trvs if there aren't any.

 

The part that does get a bit messy is where you rightly point out that in order to make the system efficient, you ideally need different dhw and ch flow temps. In my experience in many instances it's the boiler rather than the controller that causes the problem, simply because it cannot deal with this difference - it beggars belief the number of installers around me chucking in a certain model Worcester Bosch boiler despite this problem, for example. However, you can find the ones that do, even if the manufacturers might not explicitly tell you about this. I've personally gravitated towards Ideal boilers because they have a separate switched live for dhw that gives a flow temp of up to 80C and a normal switched live that can be set to 55C or lower for CH. Even better, I can install an opentherm controller to the boiler to modulate the ch but still use the 80C sl2 for hot water (it's also possible on some models to set a max boiler water temp to bring down the dhw to whatever you like, if you want). What I've been doing with system and heat only installations is reconfiguring to PDHW using a combination of normally open and normally closed diverter valves that make this system work properly, even in multi-zone installations - basically the normally open valve is used on the ch side and normally closed on dhw and when the cylinder stat calls for dhw heat, it opens the normally closed at the same to as closing the normally open.

 

For controllers I've been using either the Ideal own systems (Ideal Heat & System Halo does support priority hot water, which is good) or Honeywell, but have done and will be doing installs using Nest/Hive/Tado, usually specifically down to customer specifically asking for them. With Tado, I'm still very unhappy with how they've dealt with Opentherm here in the Uk and when I explained what was needed now - a wired unit + wireless extension, a recent customer wasn't too happy either, asking me if I couldn't just get an EU version for them.... Problem is that most customers have no idea how each individual controller works and it's difficult even as an installer to know these things properly.

 

More widely it's a total mess, a lot of installers are ignoring these new controller requirements so they're quite happy to bung in a new boiler and wire it up to existing controls and don't seem to know about modulation. I suspect it's the same for new whole system installations where it'll be rule of thumb.

 

From a customer perspective, feedback has been quite interesting. Only very recently are they asking about flow temperatures and how to best set them up, so the message is starting to get out there.

 

On 26/12/2022 at 22:31, Radian said:

I've read interesting discussions in social charity circles about the impact this change in legislation will have on home owners.

 

I've just read this. I understand the rationale behind the idea but I think they've missed a number of critical elements and is a bit misleading. For example, you won't get a replacement boiler in just 2-3 days as there's a serious shortage of installers across the whole country, and according to recent industry research only about 1/3 of existing gas engineers are planning to train to do heatpumps, leaving us in a very dire situation for resources. Yes, the boilers are most often distress decisions, but I don't think the library idea necessarily works. If a customer is going to be asked to pay £1500 for the installation of a new boiler that is expected to last for 10 years, it's a bit steep to ask them to front this cost for a leased boiler, for potentially a year or so, something that will impact poorer purchasers much more. I also think they've got to reconsider the reality of making the home heatpump ready. In many instances I think it'll take a good 10 years for this to happen and by then they're better off just purchasing a replacement boiler (from a convenience, cost and function perspective).

 

The one thing that doesn't get much air time, but has been making the rounds much more in the industry press is the hybrid heatpump/boiler, contained within a casing about the same size as your typical boiler. As a transitional idea, this is making more and more sense to me, simply because of the problems we've got with our housing stock and existing boiler install base of combis. It would also help in respect of making the boiler much better at modulating output through the year.

[Radian]

Thanks for a really interesting reply!

 

22 minutes ago, SimonD said:

With the new Part L we're technically only required to design to 55C flow temps where there is a new heating system installation. When it comes to replacing a boiler, it's about ensuring that the new one doesn't perform any worse than the one you're replacing and then that controls are installed that provide either weather/load compensation, or automisation/optomisation, or flue gas heat recovery.

 

I thought that the June update to Part L brought boiler replacements in line with the requirements for new installations, but...

 

"5.10 Where a wet heating system is either: a. newly installed b. fully replaced in an existing building, including the heating appliance, emitters and associated pipework all parts of the system including pipework and emitters should be sized to allow the space heating system to operate effectively and in a manner that meets the heating needs of the dwelling, at a maximum flow temperature of 55°C or lower. Where it is not feasible to install a space heating system that can operate at this temperature (e.g. where there is insufficient space for larger radiators, or the existing distribution system is provided with higher temperature heat from a low carbon district heat network), the space heating system should be designed to the lowest design temperature possible that will still meet the heating needs of the dwelling."

 

...on reading it again, it might only seem to apply if you were changing all (?) the radiators and pipework as well. Damn vague as you might expect from something with legal bindings. Leave one short length of original pipe and you can do what else you like.🙄

[SimonD]

20 hours ago, Radian said:

...on reading it again, it might only seem to apply if you were changing all (?) the radiators and pipework as well. Damn vague as you might expect from something with legal bindings. Leave one short length of original pipe and you can do what else you like.🙄

 

I think Part L has been done really badly. There is a separate section with the AD that details what needs to be done for boiler only replacements. I've seen there's also confusion about what impact Part L has on boiler servicing requirements. I'm completing my Part L energy efficiency and low temperature system design soon for MCS registration so I wonder whether this training will help to decipher more of the code!

[MJNewton]

21 hours ago, SimonD said:

personally gravitated towards Ideal boilers because they have a separate switched live for dhw that gives a flow temp of up to 80C and a normal switched live that can be set to 55C or lower for CH. Even better, I can install an opentherm controller to the boiler to modulate the ch but still use the 80C sl2 for hot water (it's also possible on some models to set a max boiler water temp to bring down the dhw to whatever you like, if you want). What I've been doing with system and heat only installations is reconfiguring to PDHW using a combination of normally open and normally closed diverter valves that make this system work properly, even in multi-zone installations - basically the normally open valve is used on the ch side and normally closed on dhw and when the cylinder stat calls for dhw heat, it opens the normally closed at the same to as closing the normally open

This is really good to hear actually as I am currently considering future boiler options. We have a 15yr old Ideal Icos which despite seemingly not being particularly well liked by the industry (perhaps the pre-upgraded PCB ones) has performed near perfectly for us but I am mindful it won't last forever and some upcoming renovation work might be the ideal time to consider replacing it. 

 

The Icos is married to an unvented cylinder and we'll keep this so looking for a heat only or system boiler to drop in. I was considering another Ideal (do you have any personal model preferences/recommendations?) or perhaps an Intergas. Either way it'd be in an X-plan arrangement with PDHW so dual temperature control would be welcome. We've got a Honeywell T6 controller so are Opentherm ready which would be good to exploit. 

[JohnMo]

X plan, just run weather compensation/ load compensation from the units controller, why do you need a T6 controller at all?

[MJNewton]

53 minutes ago, JohnMo said:

X plan, just run weather compensation/ load compensation from the units controller, why do you need a T6 controller at all?

It's a fair question, and perhaps part of the answer is familiarity. There are a few features such as remote control and geofencing that I'd need to work out alternative implementations of, but perhaps more so is that I'm yet to be convinced of the day-to-day effectiveness of weather compensation given variation on solar gain and wind chill etc. I'd certainly be up for giving it a try though but would make sure I had something room-temperature based to fall back on that I know first-hand works really well. 

Edited December 31, 2022 by MJNewton

[JohnMo]

There a few things to get your head around.

 

No need for geofencing or remote control, the basis is the heating runs all the time at as low a practical temp it can.  The longer the heating runs the cooler the flow temps can be.  You are trying to match heat loss with the amount of heat given from the heating system.

 

What's the point, efficiency - less gas used, due to gas to heat conversion rates above 100%, I am currently running at around 110% efficiency.  That means my DHW effectively comes free compared to running mid 90% efficiency.  Most heating system run in the high 70s to 80s% efficiency.

 

Solar gain etc.  The closer the heat emitter is to the room temperature the more self modulation that occurs. An UFH or radiator system, works by being hotter than the air around it.  The bigger the difference in temp the more heat it transfers.  The closer the temp the less heat it transfers. The boiler output modulates based on return temperature.

 

So using the above. Room at 20 degs. Sun comes out, room warms up to 23, radiator gives less heat to the room as the delta between to room and radiator has reduced, return temp to boiler doesn't drop as much, as less heat is given to the room, so boiler ramps down its output, because it tries to maintain a set DT between flow and return temp.  Radiator is then cooled.  Sun goes away room starts to cool, the reverse occurs.

 

It's taken me a year to get to here.  But I took all the actuators off the UFH manifold the other day. There were doing nothing, just powered for no good reason.

 

[MJNewton]

I'd be very interested in giving weather compensation a try, I just don't want to commit without a backup plan. Its certainly a feature I'd be wanting supported by any potential boiler choice. Got to somehow narrow the options for boiler selection down despite such contradictory reviews and opinions out there. 

Edited December 31, 2022 by MJNewton

[JohnMo]

I have an Atag, super quite, especially when doing central heating.

 

I think Viesmann boilers lets you you do two zones at different temps with different compensation curves as well a different temp for the cylinder.

 

I think the way to have a fall back is to have tcvs on the rads, but set them a couple of degrees over your normal room temp.  Then balance the system to get the room temps correct.  Worst case, you stop weather comp, set up as normal and away you go.  An X plan still gives you the ability to run the cylinder at a different or the same temp as CH.

[SimonD]

On 31/12/2022 at 12:35, MJNewton said:

I was considering another Ideal (do you have any personal model preferences/recommendations?) or perhaps an Intergas. Either way it'd be in an X-plan arrangement with PDHW so dual temperature control would be welcome. We've got a Honeywell T6 controller so are Opentherm ready which would be good to exploit. 

 

I lean towards the Vogue Max as my preference but have done a few Logic Max installs now too. I've installed some T6Rs with heat & hot water so if these have the same wiring as the earlier T6, then is fairly straight forwards. In the receiver box, wire up your heating to opentherm on the boiler (bridging the SL1 connection) and then wire the hot water switched live to SL2 on the boiler via the junction box, cylinder stat and motorized valves. I prefer using 2-port diverter valves, so have a normally closed on the dhw side and normally open on the ch side that is wired to the normally closed valves switched live so that it closes when the dhw diverter opens.

 

Intergas are good boilers but if you look at the minimum output on modulation the Ideal is slightly better, except for the 40kW intergas system boiler.

 

On 31/12/2022 at 13:22, JohnMo said:

X plan, just run weather compensation/ load compensation from the units controller, why do you need a T6 controller at all?

 

By this I'm assuming you're intending to have everything on constantly and rely entirely on the flow temperature set point to manage room temperatures? The T6 controller will provide you with some additional control, especially if you don't want your heating on all the time. I also wonder whether this setup provides less overall control of the system than load compensation using programmers/room stat/ and opentherm.

 

Ideal's own installation manual gives an ERP of 2% with weather comp on its own and 4% used in combination with a programmer.

[JohnMo]

With any WC controller you should be able to set up setbacks, where flow temp is reduced, i.e. reducing house temp.  

 

You need to careful with a lot of opentherm controllers in the UK as all they are is on/off relays. For instance to get proper operntherm control from a Tado, you need to get the European version from their website, all the rest connect to opentherm but are degraded for the UK market to on/off control.

 

A decent boiler controller should give, weather comp, load compensation and self learning stop and start optimisation.  I mine does (Atag), but you have to be careful with UFH due to the slow reaction times, but with rads you can turn it all on, almost self sets the WC curve, you set the setback times and it learns when to start flowing at at higher temp and when to flow the lowest temp.

[SimonD]

56 minutes ago, JohnMo said:

all the rest connect to opentherm but are degraded for the UK market to on/off control

 

This is simply not correct. In my experience, it's often not the controllers that are at fault, it's how they are installed.

 

When choosing a controller it's important to check the ERP rating of the controller as the combined controller and boiler ratings give the overall ERP of the boiler installation according to Part L. Below is a good explanation of the ERP classes taken from https://phpionline.co.uk/feature-articles/erp-control-classes/.

 

Class I
On/off Room Thermostat: A room thermostat that controls the on/off operation of a heater. Performance parameters, including switching differential and room temperature control accuracy are determined by the thermostat’s mechanical construction. Package/system space heating uplift = 1%

Class II
Weather compensator control, for use with modulating heaters: A heater flow temperature control that varies the set point of the flow temperature of water leaving the heater dependent upon prevailing outside temperature and selected weather compensation curve. Control is achieved by modulating the output of the heater. Package/system space heating uplift = 2%

Class III
Weather compensator control, for use with on/off output heaters: A heater flow temperature control that varies the set point of the flow temperature of water leaving the heater dependent upon prevailing outside temperature and selected weather compensation curve. Heater flow temperature is varied by controlling the on/off operation of the heater. Package/system space heating uplift = 1.5%

Class IV
TPI room thermostat, for use with on/off output heaters: An electronic room thermostat that controls both thermostat cycle rate and in-cycle on/off ratio of the heater proportional to room temperature. TPI control strategy reduces mean water temperature, improves room temperature control accuracy and enhances system efficiency. Package/system space heating uplift = 2%

Class V
Modulating room thermostat, for use with modulating heaters: An electronic room thermostat that varies the flow temperature of the water leaving the heater dependent upon measured room temperature deviation from room thermostat set point. Control is achieved by modulating the output of the heater. Package/system space heating uplift = 3%

Class VI
Weather compensator and room sensor, for use with modulating heaters: A heater flow temperature control that varies the flow temperature of water leaving the heater dependent upon prevailing outside temperature and selected weather compensation curve. A room temperature sensor monitors room temperature and adjusts the compensation curve parallel displacement to improve room comfort. Control is achieved by modulating the output of the heater. Package/system space heating uplift = 4%

Class VII
Weather compensator and room sensor, for use with on/off output heaters: A heater flow temperature control that varies the flow temperature of water leaving the heater dependent upon prevailing outside temperature and adjusts the compensation curve parallel displacement to improve room comfort. Heater flow temperature is varied by controlling the on/off operation of the heater. Package/system space heating uplift = 3.5%

Class VIII
Multi-sensor room temperature control, for use with modulating heaters: An electronic control, equipped with three or more room sensors that varies the flow temperature of the water leaving the heater dependent upon the aggregated measured room temperature deviation from room sensor set points. Control is achieved by modulating the output of the heater. Package/system space heating uplift = 5%

 

[JohnMo]

38 minutes ago, SimonD said:

This is simply not correct

Sorry it is for Tado as I stated.  It is also true if others.

 

As I believe you are aware

 

[SimonD]

16 hours ago, JohnMo said:

It is also true if others.

 

Yes I'm aware of tado and aware of the reversal in decision to bring it back, even if messily. Every other controller I install has a clear ERP label that tells me what I'm installing. The Honeywell T6 is ERP class V which is a modulating control using opentherm. Ideal Halo products are class VI, again modulating using opentherm.

 

I'm interested to hear who else you're claiming has degraded opentherm to on/off?

 

[MJNewton]

On 02/01/2023 at 13:44, SimonD said:

I lean towards the Vogue Max as my preference but have done a few Logic Max installs now too.

 

Okay, thanks - will check them out. I see there'a a Logic 2 out now so will dig deeper into what differences that brings.

 

Quote

I've installed some T6Rs with heat & hot water so if these have the same wiring as the earlier T6, then is fairly straight forwards. In the receiver box, wire up your heating to opentherm on the boiler (bridging the SL1 connection) and then wire the hot water switched live to SL2 on the boiler via the junction box, cylinder stat and motorized valves. I prefer using 2-port diverter valves, so have a normally closed on the dhw side and normally open on the ch side that is wired to the normally closed valves switched live so that it closes when the dhw diverter opens.

 

With the T6 being CH-only I was intending on continuing with a 'dumb' timer to control the DHW. Do the Ideal's still allow different flow temperatures to be set for CH and DHW (noting it knows which is calling given the separate SL1 and SL2 demand inputs, as well as the Opentherm connection)? A quick skim of the Vogue system boiler IMs suggest it might not be able to. If not I could always swap for a T6R which would presumably allow the controller to dictate these?

 

Quote

Intergas are good boilers but if you look at the minimum output on modulation the Ideal is slightly better, except for the 40kW intergas system boiler.

 

Yes, it has been an obvious downside to the Intergas offerings (that and the lack of detailed documentation - it seems a lot is missed out of the English translations). I think they drop to around 6kW (possibly less?) whereas I see these Ideal's are going down to around 3kW and indeed others like Viessmann now able to go below 2kW. I'm keen to operate 'low and slow'.

 

[JohnMo]

If you have room for a buffer and allow it to float on boiler output temp (no thermostat), min modulation isn't the end of the world.  Currently with a min modulation of 6.7kW at 30 degree, against an under 3kW demand, my efficiency gas into boiler to heat at UFH manifold is around 110%.

 

So go with the boiler you are comfortable with and is at the right price and can run X plan or priority hot water and a different CH flow temp.

[Radian]

9 hours ago, JohnMo said:

If you have room for a buffer and allow it to float on boiler output temp (no thermostat), min modulation isn't the end of the world.  Currently with a min modulation of 6.7kW at 30 degree, against an under 3kW demand, my efficiency gas into boiler to heat at UFH manifold is around 110%.

I don't understand how that works. Do you mean the boiler flow temperature is set to 30^oC? Does the buffer ever reach that temperature and if it does what return temperature is the boiler seeing?