2 programmer/thermostats on a combi?

2 programmer/thermostats on a combi?

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clockworks

Original Poster:

5,294 posts

144 months

Saturday 6th January 2018
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My sister has just moved into a 2 year old house with an Ideal combi boiler. There are 2 identical Danfoss 5/2 programmer thermostats installed, one in the lounge and one in the hallway. Pretty sure they were installed when the house was built. There are TRVs on all the radiators, but most of the heads are missing.
The wiring is all a bit weird to my eyes, especially the lighting circuit. Looks like they ran the loop into each light switch, rather than the ceiling roses. Bit confusing on a 2-way light, all done with standard T&E and choc blocks for the neutrals and earths.

Why would there be 2 programmers?
Are they just wired in parallel into the boiler?

We want to fit an Evohome setup. I assumed that the Evohome boiler relay would just wire straight up to the boiler, replacing the 'stat. The fact that there are 2 of them has thrown me a little.

caterhamboy

568 posts

197 months

Saturday 6th January 2018
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New build house require two zones for heating, so that two different heating loops to the rads.

It's common practice to loop in and out at the switches now leaving just switch wire neutral and earth to light fitting.


Edit: has the living room got underfloor heating?

AndrewO

647 posts

182 months

Saturday 6th January 2018
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2 zones would make sense. Have a look and see if you can see the control valves near the boiler/pump

Looping the lives in switches is pretty common, you still need to pick up a neutral from somewhere. Looping the live and neutral around the ceiling roses is common but if its downlights you wouldn't want to do that.

caterhamboy

568 posts

197 months

Saturday 6th January 2018
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neutral will already be at light fitting, some of the modern combi's come with facility for two zones inside ready to go.

clockworks

Original Poster:

5,294 posts

144 months

Saturday 6th January 2018
quotequote all
OK, thanks for the info. First time I've looked at a relatively new house.

It's possible that it has UFH. The lounge is quite large, and only has one relatively small radiator.
This is the first time that I've looked at a combi. It's fitted inside a standard wall unit in the kitchen, and the pipes go upwards into the ceiling.
Would a combi use the same type of external diverters that one would find on a system boiler, or are they internal? There's nothing else in the boiler cupboard, so maybe in a built-in cupboard upstairs?

I guess if it does have 2 zones, that will complicate the Evohome install. 2x BDR91's?


I was looking inside a light switch backplate because my sister wants a dimmer switch in the lounge. I figured I would try and get the existing 2 way 2 gang switches working in a logical way first - back door switch worked the light at the far end of the room (rather than the one closest to the switch), on the internal door switch, the left one worked the right light, the right switch worked the left light. Totally illogical to all of us.
I got everything switching the logical way (2 switched lives swapped over), now need to find a 2 gang dimmer that will work with LED BC pendant fittings.

caterhamboy

568 posts

197 months

Saturday 6th January 2018
quotequote all
re the dimmer just swap wires as they are L1 to L1, L2 to L2 , C to C.

yes boiler can be integral regarding valves so evo homes will just wire as normal thermostat.

Put money on ufh in living room if only small rad which will work with hall thermostat, so if underfloor off rad still on providing some heat.

clockworks

Original Poster:

5,294 posts

144 months

Saturday 6th January 2018
quotequote all
caterhamboy said:
re the dimmer just swap wires as they are L1 to L1, L2 to L2 , C to C.

yes boiler can be integral regarding valves so evo homes will just wire as normal thermostat.

Put money on ufh in living room if only small rad which will work with hall thermostat, so if underfloor off rad still on providing some heat.
Now that I've got the lights working logically, it should be a simple matter to swap for a dimmer - provided I can find one that works properly with LEDs.

OK, that does make sense. We'll have to investigate further, work out what each programmer actually operates. Presumably if one programmer/stat just works with the UFH, we could just leave that zone as it is, replacing the other one with with the Evohome kit? Just a case of finding the right stat terminals in the boiler, and wiring them to the BDR91?

Replacing the UFH programmer/stat with a BDR91 would presumably require an Evohome room stat bound to that zone?
Or is there a simpler way of doing it?


The previous tenants (it's a housing association property) didn't have a clue on how it all worked. When my sister moved in yesterday, the programmers were set correctly, but the boiler was set to hot water only, and both the hot water and heating boiler controls were set to maximum. When we eventually got the heating running, the radiators got extremely hot. All working OK now that the controls are set properly.

caterhamboy

568 posts

197 months

Saturday 6th January 2018
quotequote all
clockworks said:
Now that I've got the lights working logically, it should be a simple matter to swap for a dimmer - provided I can find one that works properly with LEDs.

OK, that does make sense. We'll have to investigate further, work out what each programmer actually operates. Presumably if one programmer/stat just works with the UFH, we could just leave that zone as it is, replacing the other one with with the Evohome kit? Just a case of finding the right stat terminals in the boiler, and wiring them to the BDR91?

Replacing the UFH programmer/stat with a BDR91 would presumably require an Evohome room stat bound to that zone?
Or is there a simpler way of doing it?




The previous tenants (it's a housing association property) didn't have a clue on how it all worked. When my sister moved in yesterday, the programmers were set correctly, but the boiler was set to hot water only, and both the hot water and heating boiler controls were set to maximum. When we eventually got the heating running, the radiators got extremely hot. All working OK now that the controls are set properly.
Yes dimmers and LEDs can be a problem.

Heating on boiler needs to be about half way 50-60 degrees so it can condense for most efficiency, ufh will prob be best with standard thermostat as the heat cycles take a lot longer.



clockworks

Original Poster:

5,294 posts

144 months

Tuesday 9th January 2018
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I got my sister to check what radiators come on with each programmer/thermostat.

The one in the lounge just controls the radiator in the lounge. There doesn't appear to be any underfloor heating (room gets cold if radiator shut off with programmer calling for heat).
The one in the hallway controls all the other radiators - kitchen, hallway, downstairs toilet, bedrooms, bathroom.

The boiler is an Ideal Logic ES35. Looking at the installation guide, it only appears to have the facility for one external programmer, and one onboard diverter valve.

I wonder how the second zone (lounge) is connected up? How does it work?

I assume that I would connect up the BDR91 relay across the "external timer" connection block, and pick up the mains supply for the BDR91 from the boiler fused spur (or the boiler mains input terminals). That would take care of all the radiators except the lounge.

The Evohome kit that we are reusing includes a second BDR91 that was used with a hot water kit (not needed with a combi). If I could figure out how the lounge zone works with it's programmer, I could use the spare BDR91 to control that. Not the end of the world if I can't, but I'd like to get everything working.

sas62

5,624 posts

77 months

Tuesday 9th January 2018
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Thats an odd setup for the two zones boiler. Normally its one upstairs and one downstairs.

clockworks

Original Poster:

5,294 posts

144 months

Wednesday 10th January 2018
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It does seem an odd way to divide up the 2 zones, but the layout of the house might explain why they didn't go for upstairs and downstairs. Both hallways are very wide (wheelchair friendly?), so much of the heat from the downstairs hallway and kitchen/diner will find it's way upstairs. The lounge is quite large, and probably the only downstairs room that would normally have it's door shut.

I'm struggling to figure out how the lounge zone works if the boiler only has one diverter and one 'stat connection though.

clockworks

Original Poster:

5,294 posts

144 months

Saturday 20th January 2018
quotequote all
Finally got to my sister's house and had a look at how the heating system is connected up. We found a couple of Danfoss 2 port valves and a wiring centre in an upstairs storage cupboard. About as far away from the boiler as it was possible to site them!

Each programmer is connected to a valve motor, the valve switches are commoned back to the boiler 'stat connections. Single flex back to the boiler. Seemed strange to my eyes, using flex for a fixed installation.

I can pick up all the BDR91 connections from the wiring centre, replacing the programmer switched live with the BDR91 switched live. The BDR91s will fit in the cupboard. Should be a simple install.

Can I use 3 core 1.0mm cable for the wiring (as I've used in the past for 2 way lighting circuits), or is there a more suitable cable? I just need L & N, plus a switched live return from each BDR91. 3 core lighting cable will obviously work electrically, just not sure of the colours required these days.

There's definitely no UFH in the lounge, just a single radiator. I went round the room with my non-contact digital thermometer, and most of the floor was at the same temperature as the internal walls. The whole house warms up very quickly, so the insulation must be very good.

We also added a couple of new light fittings and sockets upstairs. I'm beginning to see the advantage of running the lighting loop to each switch, rather than between ceiling roses. Piece of cake to run new drops inside metal stud partition walls.