Short Cycling, any advice?

[JohnMo]

4 minutes ago, Super_Paulie said:

But what advantage would I gain from this increased volume, longer cycle time?

Cycling is part volume and the other more critical is having somewhere to take heat away - the heating system. An example is trying to push low flow temps through small radiators, they just don't have enough heat transfer area to transfer the energy generated to the room. So heat source cycles as that is all it can do. In this situation you would install radiators with about 3 to 4 times the surface area and the system works.

 

Your system is having a first cycle helped by having to heat a bigger volume (volumiser). But you are not really dumping the heat to the house, I suspect the heat loading in the floor is running full, the house heat loss is way smaller than the continuous heat being supplied.

 

The heat flow through your UFH is about 1.2kW per loop. But depending on room heat losses a lot of this will be recycled water, so may not all come from the boiler.

 

So 4x loops at 2.5 l/min, so y

 

8 minutes ago, John Carroll said:

7C dT,

The Salus actuator will target that dT.

 

Suggested action

Leave system as is

Manually switch off boiler or UFH until house cools to about 20, then switch boiler or UFH back on again see what happens. If you get a long run your solution couple simply batch charge the floor - use as a storage heater.

[John Carroll]

42 minutes ago, Super_Paulie said:

Yeah it's dead on 7 lower, the actuators see to that and seemingly work a treat.

 

42 minutes ago, Super_Paulie said:

Yeah it's dead on 7 lower, the actuators see to that and seemingly work a treat.

So, the return temp to the boiler must be 41C, the (boiler) flow temp is 60C, dT, 60-41, 19C, UFH dT, 48-41, 7C, boiler flowrate, 10*7/19, 3.68LPM, so there obviously is HW being recirculated to give that higher return temp, the only downside of this is that the boiler efficiency will be lower at the higher return temp so maybe just look at this, rather than trying to get longer cycle times etc by creating a bigger heat demand or whatever, your system is, IMO, performing very well, why not leave it be.

 

The "picture" below might be easier to understand UFH mixing etc and you can do your own calcs.

UFH Calculations with Bypass Extract Rev0.xlsx

Edited Wednesday at 23:22 by John Carroll

[John Carroll]

Slight change to Spreadsheet as one value couldn't be changed without unprotecting the sheet.

 

UFH Calculations with Bypass Extract Rev1.xlsx

Edited Thursday at 07:57 by John Carroll

[marshian]

13 hours ago, John Carroll said:

The (any) boiler  should not refire until the flow temp is target temp - 5C, 60-5, 55C in this case, any modulating boiler cannot work if either the cut in/cut out are  at  target temp.

 

My flow temp last night at 6 deg C was 30 deg C

The boiler over the course of 15 mins gradually went over target temp at min modulation 10.6% (3.2 kWh) by 4 deg in order to extend the run time so finally shut down at 34 Deg C

 

I wasn't busy so watched my temp sensors for the 20 mins it coasted (pump running boiler not firing) and it re-fired shortly after this picture was taken.

 

Left side display is flow temp

Right hand side is return temp

 

 

I'm pretty sure my boiler doesn't follow the flow temp - 5 deg rule

 

My previous glow worm boiler didn't either

[John Carroll]

1 hour ago, marshian said:

 

My flow temp last night at 6 deg C was 30 deg C

The boiler over the course of 15 mins gradually went over target temp at min modulation 10.6% (3.2 kWh) by 4 deg in order to extend the run time so finally shut down at 34 Deg C

 

I wasn't busy so watched my temp sensors for the 20 mins it coasted (pump running boiler not firing) and it re-fired shortly after this picture was taken.

 

Left side display is flow temp

Right hand side is return temp

 

 

I'm pretty sure my boiler doesn't follow the flow temp - 5 deg rule

 

My previous glow worm boiler didn't either

Yes, theoretically, the boiler should be able to refire once the flow temp falls to its target setting, the burner cut out has to be higher than the target temp otherwise the burner would cut out every time the target temp is reached, it is usually set at 5C to allow a little overshoot without tripping the burner on fire up and sudden target temp changes, a decrease in target temp > 5C below the flow temp will usually trip the burner as well.

Is your target temp 30C? and what is the anticycle time set to? is it like the Vaillan't look up table or exactly as you input it, ie a 3 min anticycle time is exactly 3 minutes?.

 

[marshian]

25 minutes ago, John Carroll said:

Yes, theoretically, the boiler should be able to refire once the flow temp falls to its target setting, the burner cut out has to be higher than the target temp otherwise the burner would cut out every time the target temp is reached, it is usually set at 5C to allow a little overshoot without tripping the burner on fire up and sudden target temp changes, a decrease in target temp > 5C below the flow temp will usually trip the burner as well.

Is your target temp 30C? and what is the anticycle time set to? is it like the Vaillan't look up table or exactly as you input it, ie a 3 min anticycle time is exactly 3 minutes?.

 

 

The boiler is set up to run on WC for CH with DHWP

 

Only parameters that I have found and adjusted to suit the house and optimise the boiler are only applicable to CH (DHWP are max output (19kWh) and  max flow temp (82 Deg C).

 

Max Water Temp Limit 70 Deg C

Max Output 40% (so 8 kWh because anything more is not needed - I may drop this further to around 6 kWh)

 

No Anti-cycle parameters that I have found

 

Pump Over run is non adjustable (set to a 3min max from factory)

 

I'd attach the Installation and operation manual but it's too large but a google for Viessmann 100-W B1GA should get you to a copy

 

The Valliant (Glow worm) Anti-cycle parameters took me for ever to get my head around but once I did it was very useful and getting a 24 kWh boiler with a 10 kWh min to work much better with less cycling! (mainly because I was also using pump overrun to manage the time between burns as well)

 

 

 

[Super_Paulie]

7 hours ago, John Carroll said:

Slight change to Spreadsheet as one value couldn't be changed without unprotecting the sheet.

 

UFH Calculations with Bypass Extract Rev1.xlsx 15.77 kB · 1 download

John, thanks a lot. Ive been trying to get my head around this on my lunch at work but i just cant comprehend it, im just not educated in boiler flows im afraid. Im not sure what numbers to change to "make this better" so my apologies. Your effort is way beyond the call of duty, but im a mere mortal 😆

 

So it looks like a "low and slow" way of doing business isnt going to work for me due to not having a boiler than can modulate down far enough, but rather a "batch heating" of the floor just when i need it and accept a 15 minute(ish) cycle time, thats no problem as thats what i was doing until a few weeks back.

 

Having this at a 60 degree flow, 45 mixer is ultimately higher than i wanted on both sides but that gives me a cycle time of around 12, lets say 15 minutes. I have it with a very small bypass rad currently and my house IS warm enough but ultimately i am heating a water tank in the loft that is just sitting laughing at me asking for more money. 

 

If there is any way i can get this flow rate down without the system cycle or am i just at the limit due to the boiler?

I will be getting a bigger rad and snaking the return under the bathroom floor as a makeshift UFH, that wont add a huge amount of volume but it would take more heat away.

 

Ok, so this costs a few quid a day to keep my family warm, im not going to lose any sleep over that. Thanks so much guys, what a great forum this is and has been in my build so far.

[John Carroll]

45 minutes ago, Super_Paulie said:

John, thanks a lot. Ive been trying to get my head around this on my lunch at work but i just cant comprehend it, im just not educated in boiler flows im afraid. Im not sure what numbers to change to "make this better" so my apologies. Your effort is way beyond the call of duty, but im a mere mortal 😆

 

So it looks like a "low and slow" way of doing business isnt going to work for me due to not having a boiler than can modulate down far enough, but rather a "batch heating" of the floor just when i need it and accept a 15 minute(ish) cycle time, thats no problem as thats what i was doing until a few weeks back.

 

Having this at a 60 degree flow, 45 mixer is ultimately higher than i wanted on both sides but that gives me a cycle time of around 12, lets say 15 minutes. I have it with a very small bypass rad currently and my house IS warm enough but ultimately i am heating a water tank in the loft that is just sitting laughing at me asking for more money. 

 

If there is any way i can get this flow rate down without the system cycle or am i just at the limit due to the boiler?

I will be getting a bigger rad and snaking the return under the bathroom floor as a makeshift UFH, that wont add a huge amount of volume but it would take more heat away.

 

Ok, so this costs a few quid a day to keep my family warm, im not going to lose any sleep over that. Thanks so much guys, what a great forum this is and has been in my build so far.

You really can't do anything about the cycling due to the boiler's minimum output being higher than the heat demand but so what?, your boiler isn't short cycling which I I would term a boiler which can't get away without multiple firings and fires for only a minute or so like yours was previously, its grand talking about low and slow when/if you have a boiler that can modulate down to a couple of kw, cycling will cost a few quid more in fuel costs but I wouldn't be rushing off to buy a Viessmann or such like to achieve this especially if your present boiler is reliable,  some worry about the extra wear and tear but this doesn't worry the users of smart CH systems like Evohome which can cycle the boiler up to 6 times/hr (more often than yours) even when the heat demand exceeds the boiler's minimum output.

I have a nearly 20 year old oil boiler that must have cycled thousands of times (because it cant modulate) and it hasn't cost a single cent in repairs, I dare say there are plenty of gas boilers likewise that continually cycle and run for years without any repairs.

 

Anyhow I've attached a modified spreadsheet that I put together for someone with a Vaillant Ecotec 630 boiler with a low loss header that will only run properly in one mode of operation, it may be of interest, if nothing else.

You will notice in the sheet "UFH Only with Bypass" that you have a bypass flow of around 3.3LPM which you may be able to reduce a little without compromising the boiler firing and reduce the return temp from its present ~ 50C to say 45C or so which would lead to a nice bit of extra condensing and greater boiler efficiency.

UFH + Rads Extract Rev0.xlsx

[MJNewton]

1 hour ago, John Carroll said:

some worry about the extra wear and tear but this doesn't worry the users of smart CH systems like Evohome which can cycle the boiler up to 6 times/hr (more often than yours) even when the heat demand exceeds the boiler's minimum output.

I have a nearly 20 year old oil boiler that must have cycled thousands of times (because it cant modulate) and it hasn't cost a single cent in repairs, I dare say there are plenty of gas boilers likewise that continually cycle and run for years without any repairs.

 

Yeah, I was always concerned about Honeywell's TPI control algorithm which, whilst excellent at minimising (effectively eliminating) overshoot/undershoot does so at the expense of upto 6 demand cycles per hour (actually, writing that down I think it can be lowered to 3). I've been expecting having to deal with the consequences of additional wear this will have on the system for 14 years now but so far, touch wood, no failures to report.

Edited Thursday at 19:18 by MJNewton

[Super_Paulie]

2 hours ago, John Carroll said:

You really can't do anything about the cycling due to the boiler's minimum output being higher than the heat demand but so what?, your boiler isn't short cycling which I I would term a boiler which can't get away without multiple firings and fires for only a minute or so like yours was previously, its grand talking about low and slow when/if you have a boiler that can modulate down to a couple of kw, cycling will cost a few quid more in fuel costs but I wouldn't be rushing off to buy a Viessmann or such like to achieve this especially if your present boiler is reliable,  some worry about the extra wear and tear but this doesn't worry the users of smart CH systems like Evohome which can cycle the boiler up to 6 times/hr (more often than yours) even when the heat demand exceeds the boiler's minimum output.

I have a nearly 20 year old oil boiler that must have cycled thousands of times (because it cant modulate) and it hasn't cost a single cent in repairs, I dare say there are plenty of gas boilers likewise that continually cycle and run for years without any repairs.

 

Anyhow I've attached a modified spreadsheet that I put together for someone with a Vaillant Ecotec 630 boiler with a low loss header that will only run properly in one mode of operation, it may be of interest, if nothing else.

You will notice in the sheet "UFH Only with Bypass" that you have a bypass flow of around 3.3LPM which you may be able to reduce a little without compromising the boiler firing and reduce the return temp from its present ~ 50C to say 45C or so which would lead to a nice bit of extra condensing and greater boiler efficiency.

UFH + Rads Extract Rev0.xlsx 1.91 MB · 0 downloads

 

Very interesting, thanks. 

I've looked to see if I can edit the anti-cycle time on my Baxi, but alas that seems not an option.

 

How could I reduce the bypass flow rate, just via the boiler flow? I am trying out 57° this evening which is giving me that lower return. Like I say, that thing is tiny but so is the room. It's toasty in there though now my flow temperature is up at 57°, actually warms the top floor if I leave the door open.

Edited Thursday at 20:24 by Super_Paulie

[John Carroll]

27 minutes ago, Super_Paulie said:

 

Very interesting, thanks. 

I've looked to see if I can edit the anti-cycle time on my Baxi, but alas that seems not an option.

 

How could I reduce the bypass flow rate, just via the boiler flow? I am trying out 57° this evening which is giving me that lower return. Like I say, that thing is tiny but so is the room. It's toasty in there though now my flow temperature is up at 57°, actually warms the top floor if I leave the door open.

Via the by pass rad, I think you said a rad valve was 3/4 of a turn open?, try a 1/4 to a 1/2 turn open.

[Super_Paulie]

Just now, John Carroll said:

Via the by pass rad, I think you said a rad valve was 3/4 of a turn open?, try a 1/4 to a 1/2 turn open.

I can do that. Sorry John, my understanding of flow rates seemingly can't be solved. I'll open up that shield a touch and see what that brings my return down to.

[John Carroll]

9 minutes ago, Super_Paulie said:

I can do that. Sorry John, my understanding of flow rates seemingly can't be solved. I'll open up that shield a touch and see what that brings my return down to.

Close it down a touch, clockwise.

[Super_Paulie]

35 minutes ago, John Carroll said:

Close it down a touch, clockwise.

Ha ha, my understanding gets worse 😆. I thought that by opening it up it would emit more heat and thus bring down the return temp. Think I'm beyond saving at this point. I'll knock that lock down now 👍

[marshian]

3 minutes ago, Super_Paulie said:

Ha ha, my understanding gets worse 😆. I thought that by opening it up it would emit more heat and thus bring down the return temp. Think I'm beyond saving at this point. I'll knock that lock down now 👍

 

No the opposite - the more open you have a lockshield the more flow it allows - therefore the more likely the return flow temp is higher - the rad may emit more heat but it's only because the meant water temp has increased. It doesn't sound like you need more heat and your boiler doesn't need a higher return temp.

[Super_Paulie]

Ok I've made that adjustment. I'm up to temperature now so I can't really get any numbers but hopefully I'm heading in the right direction. I did see that my cycle times were getting smaller with every cycle, my last cycle time I recorded this evening was quite short, 57 boiler, 45 mixer, 8 minute cycle.

[marshian]

53 minutes ago, Super_Paulie said:

Ok I've made that adjustment. I'm up to temperature now so I can't really get any numbers but hopefully I'm heading in the right direction. I did see that my cycle times were getting smaller with every cycle, my last cycle time I recorded this evening was quite short, 57 boiler, 45 mixer, 8 minute cycle.

still less than 6 cycles an hour if it’s 8 min burn 3 min coast

 

any boiler is going to cycle more when house is up to temp as it’s only going to need to replace heat lost - good tine to do a few meter reads to give you a goid idea of your heat loss at whateve OAT it is now

[John Carroll]

9 hours ago, Super_Paulie said:

Ok I've made that adjustment. I'm up to temperature now so I can't really get any numbers but hopefully I'm heading in the right direction. I did see that my cycle times were getting smaller with every cycle, my last cycle time I recorded this evening was quite short, 57 boiler, 45 mixer, 8 minute cycle.

Can you post the readings again from the UFH manifold after say 5 minutes of burner firing. also boiler flow/return temps and any other temperature readings to hand.

If its 5min ON/3min OFF cycle then the UFH demand is  ~ 6*5/8, 3.75kw, minimum.

Also try and note the boiler flow temp when it fires up and the exact time it takes to reach its maximum temp before modulating/reducing to 60C or so, it will then rise to 65C and burner trip/cycle.

 

 

Edited yesterday at 07:45 by John Carroll

[burgessl]

I remember the old Potterton boiler we had (basically a Baxi) behaved like this - once up to temp the burner would shut off for a few minutes with the pump still running, then ignite again and repeat.

 

Checking it looks like the 3 minute anti-cycle time does seem to be fixed on the Baxi boilers - a snippet I found in the manual:

Quote

When the flow temperature exceeds the set temperature, a 3 minute delay occurs before the burner relights automatically (anti-cycling). The pump continues to run during this period.

 

 

[Super_Paulie]

2 hours ago, John Carroll said:

Can you post the readings again from the UFH manifold after say 5 minutes of burner firing. also boiler flow/return temps and any other temperature readings to hand.

If its 5min ON/3min OFF cycle then the UFH demand is  ~ 6*5/8, 3.75kw, minimum.

Also try and note the boiler flow temp when it fires up and the exact time it takes to reach its maximum temp before modulating/reducing to 60C or so, it will then rise to 65C and burner trip/cycle.

 

 

 

I can do that tonight when i get back in, no problem. When i first started testing last night, the system had been on for a few hours that the cycle time had a decay after every cycle, down from 15 minutes when i started to around 8 by time the system went off.

Should i be taking my readings once the system is up to temperature but still calling, say after an hour of running?

 

Also the flow and return temps, should i take them at the boiler, so the flow reading on the screen and the return reading from my probe (after the buffer)? I was under the impression after the boiler has stopped firing the screen will then be showing the return temp rather than the flow as there is no flow. Could be wrong on that.

 

I have made a daft spreadsheet table to record what i think might help out.

Thanks loads you guys.
 

boilerTemps.xlsx

[John Carroll]

5 minutes ago, Super_Paulie said:

 

I can do that tonight when i get back in, no problem. When i first started testing last night, the system had been on for a few hours that the cycle time had a decay after every cycle, down from 15 minutes when i started to around 8 by time the system went off.

Should i be taking my readings once the system is up to temperature but still calling, say after an hour of running?

 

Also the flow and return temps, should i take them at the boiler, so the flow reading on the screen and the return reading from my probe (after the buffer)? I was under the impression after the boiler has stopped firing the screen will then be showing the return temp rather than the flow as there is no flow. Could be wrong on that.

 

I have made a daft spreadsheet table to record what i think might help out.

Thanks loads you guys.
 

boilerTemps.xlsx 10 kB · 2 downloads

Take as many readings as you can from all sources when the heating has been on for say a hour, also the ufh manifold flowrates. A cycle is the burner ON time + the boiler OFF time, can you note both of these.

 

[JohnMo]

I've a strong suspicion you are just going around in circles. You change lots and still have shortish cycles as you dump more and more heat into the floor. You need to allow the floor to buffer heat, then STOP adding more heat.

 

Your current approach is like driving a powerful car against a speed limiter. I'm

 

My approach is set thermostat at 21 to force start boiler. Let it run chasing 21 for about 4 hrs, then reduce thermostat to 20.5, for an hour or 2. Most the time the boiler switches off when the thermostat is moved to 20.5. Then set to 20, boiler switches off. Once set to 20 the floor stabilises and you get some overshoot as the floor releases it's energy. Our heating stopped at 7.30 this morning and by 11 the house was sitting at 20.7.

 

Depending on heat loss, area and depth of screed you may need to heated once or twice a day heats. But it gives a huge heat sink for the boiler to work against. In reality excluding solar gain we have less than 0.5 Deg fluctuations in temperature.

[John Carroll]

If you just leave the UFH run 24/7, what do you think your UFH system would stabilize at, heat output wise? and/or using the OPs actual data of a few posts back of UFH flowrate of 10LPM with flow/return of 48C/41C, output 4.88kw, would you expect this to stabilize at, assuming no or little change in OAT?. I thought running UFH 24/7 is the preffered way even though it obviously won't give steady room temperatures.

[JohnMo]

34 minutes ago, John Carroll said:

If you just leave the UFH run 24/7, what do you think your UFH system would stabilize at, heat output wise?

Heat output is related to overall floor surface temp and room temp. The close they get the lower the floor output. Further apart they are, the more the output.

 

34 minutes ago, John Carroll said:

I thought running UFH 24/7 is the preffered way

I run the circulation pump all the time 24/7. But control the heat input so the boiler or heat pump can cope. I have both and both, and both are oversized for heat demand - just like @Super_Paulie boiler is.

 

34 minutes ago, John Carroll said:

UFH flowrate of 10LPM with flow/return of 48C/41C, output 4.88kw

That fine, but if the boiler output minimum is more than that, the boiler cycles. @Super_Paulie changes flow temp, boiler runs until floor is heat soaked. Boiler has little or no space to add more heat. Runs a short period stops a short period repeat, as boiler tries to stuff more heat in, but cannot.

 

Imagine the floor is a battery, stick on charge, charger runs for a long period to get battery in a charged state. Then blips on off all the time it's connected. If your floor isn't giving off the heat equal to heat supply it's just the same. Messing with flow rates isn't going to make it better, you need to allow the floor to dump some energy then recharge it..repeat. At the moment the boiler is trying to do that, but not doing very good job. It needs assistance and a simple thermostat is needed or use what you have, bring thermostat down to 21 and see what it does.

[Super_Paulie]

1 hour ago, JohnMo said:

Heat output is related to overall floor surface temp and room temp. The close they get the lower the floor output. Further apart they are, the more the output.

 

I run the circulation pump all the time 24/7. But control the heat input so the boiler or heat pump can cope. I have both and both, and both are oversized for heat demand - just like @Super_Paulie boiler is.

 

That fine, but if the boiler output minimum is more than that, the boiler cycles. @Super_Paulie changes flow temp, boiler runs until floor is heat soaked. Boiler has little or no space to add more heat. Runs a short period stops a short period repeat, as boiler tries to stuff more heat in, but cannot.

 

Imagine the floor is a battery, stick on charge, charger runs for a long period to get battery in a charged state. Then blips on off all the time it's connected. If your floor isn't giving off the heat equal to heat supply it's just the same. Messing with flow rates isn't going to make it better, you need to allow the floor to dump some energy then recharge it..repeat. At the moment the boiler is trying to do that, but not doing very good job. It needs assistance and a simple thermostat is needed or use what you have, bring thermostat down to 21 and see what it does.

i understand this. No matter what i set that flow to the floor will eventually fill up, quicker or slower based on flow temp, and at that point im back to square one. Just like when i tried it low and low and then hot and fast, my usage was nigh-on identical. So no matter what i do to this my efficiency is going to be the same, its about finding the point where im condensing for longer i suppose to try and win back a few pennies and not ruin the boiler through super-low cycles?