Completely confused over heat/water controls

[Loz]

Hi,

 

Been a great forum for all my problems thus far but managed to completely confuse myself over how to control heating/water.  In midst of a renovation and what going to end up with is two zones of underfloor heating downstairs and the rest of the radiators separate.  Gone for a Baxi 824 system boiler (which is open therm compatible) and unvented gledhill tank.  The boiler is in the garage next to the manifold for the underfloor heating and the tank is in airing cupboard where the ancient timers/controls are with a thermostat nearby.  Can run wires to anywhere at moment and wanted to go for a wired system.  Don't really need wifi/app access or anything and wanted to avoid anything wireless.

 

Now this is where completely confused as started looking at what to use to control it all, plumber normally uses nest/hive with wireless stats but as above wanted to go a bit old school and have everything wired, did want to take advantage of the open them capability of the boiler.

 

Looked at all the major manufacturers Honeywell, Drayton, Nest, Tado and more but struggling to find a wired solution that can control 3 channels (open them boiler, hot water and 2 zones underfloor heating).  There are I believe 3 two port valves going into the airing cupboard where the tank is.

 

Found this programmable stat Honeywell T4M which is open therm and wired to boiler - but then how do I control the underfloor heating and water tank ?  Can I just add a 2 channel timer for those but how would they link to thermostats and how would it interact with the T4M which is linked to the boiler.  I really am confused.  Found this 3 channel programmer Horstmann Plus 3 Channel Programmer H37XL but how does that then link into thermostats and possibly achieve open therm.  As you can tell I am a bit clueless on this side and some basics would be most useful.

 

Many thanks,

 

Lawrence  

 

 

 

 

[ProDave]

Are you wanting detail to wire it yourself?  Or a baic idea for a competent electrician to do it?

 

I will start with basics.

 

3 channel timer like the Horstman (under floor heating, radiators  and hot water)

 

The UFH needs a simple generic WIRED manifold controller, whoever supplies the manifold should be able to supply that.  This takes a heat demand in from one channel of the programmer.  The UFH zone thermostats connect to this controller each with 1mm 3 core & earth cable to wired thermostats.  The manifold controller gives a "call for heat" output which drives a local 2 port motorised valve.  The switch in the motorised valve gives the call for heat to the boiler (as do others)

 

The rest is bread and butter stuff for a plumber and electrician.  The other 2 channels of the 3 channel programmer connect to the radiators and HW in a standard S plan configuration each with a 2 port motorised valve. the radiator circuit will usually have one wired room thermostat and the HW will use the cylinder thermostat.  The switch in both these 2 motorised valves connects in parallel with the one from the UFH to call for heat from the boiler.

 

If looking for tradesmen to do this, find some that properly understand heating.  If they need spoon feeding details like this, then they will be out of their depth if it does not work as expected.

[billt]

An additional point of confusion which tripped me up when I wanted to use Opentherm. Opentherm controllers don't necessarily work with all boilers, in particular they seem to be setup to work with combi boilers; system boilers are a bit of a nightmare.

 

I found this out when I tried to use a Drayton Wiser controller with a Viessman 100 system boiler. they both claimed to be Opentherm compatible, but they don't work together. In particular they don't communicate about hot water heating. The boiler needs to be set to high flow temperature when heating water rather than modulated down when heating radiators.

 

I see from the Honetwell T4-M manual that it doesn't support DHW - although the T^-RHW does.

 

Having played with a few options I'm not convinced that Opentherm offers much in reality. There's a weather compensation option on the boiler whihc does more or less the same thing.

[Loz]

Many thanks for both taking time to reply, I have an electrician and plumber who will both be on site tomorrow and was trying to get head round it so can ask the right questions as they kind of leaving the choice of programmers/thermostats to me.  The electrician has run wires for the underfloor heating thermostats back to the UFH manifold which is in the garage saying there will need to be some sort of controller there to open and close the manifold valves.  The plumber seemed a bit confused by this thinking they should be going to the airing cupboard where the two port valves are, not sure who is right here.

 

Could they connect the Honeywell T4M which is just for open therm boiler to the 3 channel timer ?  Reading literature seems to suggest this should be going to direct boiler and is programmable.  If I had a two channel timer for tank and UFH and then the T4M for the boiler how would they know about each other to operate the 3 2 port valves correctly - as you can probably tell I do not really understand this.

 

Many thanks,

 

Lawrence

 

 

[Temp]

33 minutes ago, Loz said:

The electrician has run wires for the underfloor heating thermostats back to the UFH manifold which is in the garage saying there will need to be some sort of controller there to open and close the manifold valves.

 

+1 That's what @ProDave means by...

 

1 hour ago, ProDave said:

The UFH needs a simple generic WIRED manifold controller, whoever supplies the manifold should be able to supply that.  This takes a heat demand in from one channel of the programmer.  The UFH zone thermostats connect to this controller each with 1mm 3 core & earth cable to wired thermostats.  The manifold controller gives a "call for heat" output which drives a local 2 port motorised valve.

 

33 minutes ago, Loz said:

The plumber seemed a bit confused by this thinking they should be going to the airing cupboard where the two port valves are, not sure who is right here.

 

Electrician is right. They are normally mounted near the manifold as they control the loop valves. Typically they have quite a few wires..

 

One from each room stat

One to each valve on the manifold

One from the time clock/programmer.

One to the two port valve (sometimes this goes direct to the boiler and is called "Boiler Enable" or "call for heat" it's the logical OR of the room stats).

One to the loop pump on the manifold (also logical OR of the room stats)

Possibly one from an over temperature sensor on the manifold mixer.

 

 

Edited November 4, 2021 by Temp

[Loz]

Magic, thanks for clarifying both on the controller for manifold, will try and go through it all with both of them on site,  still not sure on this side of it:

 

'Could they connect the Honeywell T4M which is just for open therm boiler to the 3 channel timer ?  Reading literature seems to suggest this should be going to direct boiler and is programmable.  If I had a two channel timer for tank and UFH and then the T4M for the boiler how would they know about each other to operate the 3 2 port valves correctly - as you can probably tell I do not really understand this.'

 

Many thanks,

 

Lawrence

[ProDave]

This is just one example of a manifold controller.  As above it takes the individual thermostat inputs and conrolls the pumps and actuators on the manifold.  this goes right next to the manifold.

 

https://www.ebay.co.uk/itm/323201244988?epid=1549854398&hash=item4b404b9f3c:g:VBsAAOSwpLNX86pn

[Loz]

2 minutes ago, ProDave said:

This is just one example of a manifold controller.  As above it takes the individual thermostat inputs and conrolls the pumps and actuators on the manifold.  this goes right next to the manifold.

 

https://www.ebay.co.uk/itm/323201244988?epid=1549854398&hash=item4b404b9f3c:g:VBsAAOSwpLNX86pn

 

Thanks for that, think that was what electrician was expecting,

 

Lawrence