Central heating zonal control fault

[Edufixer]

I have an annex with a wheel thermostat which when installed a few years ago I was told it would stop and start the oil boiler and the radiators in the annex independent of the main house. Now we are using the annex more it is apparent that this is not the case and the annex radiators will only come on when the main house is on. Is this an easy fix? Is it the wiring between the programmable unit in the main house and the annex? Thoughts would be much appreciated

 

[CBW]

It seems to me you would need the wiring configuration to a thermostat, zone valve and at the programmer, independently from the house. Although you may need a separate programmer for the annex? And your system would usually need to be an S plan.

@stem and @ericmark are usually good with these.

 

[ianmcd]

only if the thermostat is connected to ancillary controls like a zone valve you dont give enough information to get the correct advice

 

[stem]

I have frequently been called to look at similar problems, where the householder believes there is a fault with the controls. If the system used to work correctly, then the controls could be at fault. Usually in this case there is a failure of a microswitch inside a motorised valves. The valve opens OK, but the boiler doesn't start because the microswitch has failed. When another valve opens, the switch in that operates, and the boiler fires up thus supplying both zones. and creating the symptoms you describe.

However, if the fault has always been there, it is more likely that when the system was extended, the new radiators were tapped into the pipe feeding the existing radiators nearby because it's easier to do, instead of being connected back to the start of the hot water distribution (usually just after the pump). Then a motorised valve is added to the branch going out to the extension, and a thermostat fitted to that. But the main house heating also has to be operating because the extension is connected to it.

So first of all there is the clue. If the fault has always been present, it could well be a plumbing issue, if it used to work OK, and the fault developed later, it will be the controls.

As @ianmcd says you don't really give us a lot to go on.

 

[ericmark]

I am about to cure that problem with my own house, it in my case needs the adding of a relay. However the house was when we bought it in a right state as far as central heating control went.

In my case there were two independent pumps, one for flat and one for main house, plus thermosyphon for domestic hot water. It did not work as if just one pump was used it would cause a reverse flow on the other system, there were a few ways to cure it, one was non return valves, the other was motorised valves, I selected the latter, however it left a problem. If I want to ensure the pump only runs when the valve is open then using the micro switch for that, so there was no micro switch available to run the boiler, so I intend to fit a relay.

I would have preferred one pump and two valves, but the plumber wanted to retain the two pumps.

It took a combined effort between myself and the plumber to work out what I had, there were isolation valves on the pumps, so the test was to turn off the valve to prove putting a motorised valve would work, as near impossible to trace pipework, it was the problem with control which forced me to learn about central heating.

Be it an annex or just up and down stairs there are three ways to get independent control.
1) Twin pumps. (Would need non return valves)
2) Twin motorised valves.
3) Using the thermostatic radiator valve (TRV) heads.

So already talked about twin pumps and motorised valves, so the easy method may be to use the existing TRV so if we consider one large system covering house and annex then you would need two on/off wall thermostats or timers wired in parallel so either can cause the boiler to run. The TRV heads can be replaced with electronic heads which can then be set to stop either the main house or annex radiators getting hot, best would be the TRV heads linked to thermostat, but it could be done without.

I fitted eqiva eQ-3 bluetooth heads to some of my radiators, although I did not want the feature, I noted when setting up you can link the heads so they work as groups, so one group could be annex, and other group the main house. At £15 each that's the cheap way, but reading through the reports Drayton Wiser, and Hive both do a system where the TRV head tells the thermostat when to call for heat, as does Tado and Evohome, I have Nest which works with Energenie TRV heads, I have had problems getting the heads to follow the thermostat.

So I am sure it can be done, however first you have to work out what you already have, and then you need to decide which system to go for, it does seem that EvoHome gets very few complaints and has been out for a long time, but the rest is seems like sticking a pin in when blind folded as there seems to be complaints about most of the systems, and I personally feel I wasted my money on Energenie and that eqiva eQ-3 bluetooth would have done same job for a 1/3 or less of the price.

 

[Edufixer]

Thanks for all the suggestions. I now think that the issue was probably always there, but as we didn't use the annex much then it wasn't apparent. I have changed the central heating motorised switch in the last few years in the main house. The CH in the main house has an awful system whereby radiators fill up one by one, so no flow and return.
I believe I have a s plan system 1 motorised valve for ch and one for hot water. The annex has wheel thermostat on the walk only which does not start the boiler. It used to have a programmable timer but as the person in the annex was old she changed it. Could this be the reason I could change it back? I don't think so unless it controls the whole ch system as I can only find one motorised valve. I have checked electrical supply and this is coming from the junction box in the main house for the ch/hot water. This is in a very old inadequate junction box with unsheathed wire hanging out and I will replacing it with correct 10 fitting junction box. Thoughts on my options moving forward as I need to get the heating on in the annex without heating the whole of the 5 bed house it is attached to.
!

 

[stem]

I believe I have a s plan system 1 motorised valve for ch and one for hot water

OK that sounds like a standard S-Plan system.

The annex has wheel thermostat on the wall only which does not start the boiler

What is it wired to? This all depends upon the layout and design of the original wiring and the plumbing system to which it is connected. Without this information we can only guess. So you need to tell us how the thermostat is wired, and what is connected to the other end of the wires.

It used to have a programmable timer but as the person in the annex was old she changed it. Could this be the reason I could change it back?

Thermostats are just a simple on / off switch. Programmable thermostats allow you to change the time and temperature, thermostats just the temperature, but that's down to their internal workings. As far as the wiring is concerned they are both just a simple on/off switch and interchangeable. However the question is, was it wired in correctly when it was changed? So we are back to what is on the other end of it?

 

[Edufixer]

Thanks for answer, I have rewired different ways with no change. I have checked power and this is coming from the power supplied to the main CH unit in the house.
Looking at the configuration I have i believe I would need to add a second motorised valve which would be controlled from the programmable timer in the annex. What do you think

 

[stem]

The first thing to check is where the annex radiator pipes originate from. If they are simply connected to the main house radiator circuit then they will only ever heat up when the main house heating is on, even if you were to add another motorised valve. That's a restriction of the plumbing. [I'm not saying that is the case, but it's the first thing to check.]

For independent control of the annex heating, the pipe supplying the annex radiators should originate from the start of the hot water distribution (usually just after the pump). If you find that the plumbing is in order, you could then add another motorised valve at this point just for the annexe.

As you haven't located another motorised valve, it then begs the question. What is the annex thermostat presently wired to? From your first post it would appear to have worked at some point, if so it's connected to something somewhere.

 

[Edufixer]

I have found 2nd pump motorised pump and junction box. The thermostat does not start up pump, motorised valve. Oil boiler is on the outside wall behind the picture. When main house ch started then nothing happens when thermostat starts in annex the water just feeds through. Put some images up below

 

[ericmark]

I found only way was to make a diagram showing what you have, then trace what should happen.
I have made a mistake, which I need to cure.

I added a relay to allow flat to run without house, however if you trace it, you will see if flat runs then it will also energise house pump, I need to move pump from 13 to 4 until a second relay added. Without drawing it all out, it is near impossible to find where the error is.

 

[Edufixer]

Thanks to the input. I was just thinking I should do just that!

 

[stem]

What you have posted looks like a professional installation. So, you may have everything in place, but something has failed.

For example, the room thermostat should open the motorised valve to allow water to flow to the annex radiators and start the pump. When the valve is fully open it operates a small microswitch inside that should start the boiler (via the orange wire in the diagram posted by ericmark) These switches can fail and so the valve opens as it should, but doesn't start the boiler, so nothing happens. Then when the main house heating comes on, the main house valve triggers the boiler and both the main house and annex (because it's valve is open) heat up. - That would be one theory that would fit your symptoms.

A basic test of the valve would be: With the annex heating 'off' slide the manual lever on the side of the valve, you should feel resistance as you move it. Now turn the annex heating on, with someone listening next to the valve and they should hear a 'click' after 20 seconds or so. That is the switch operating. The operating lever should now be loose and floppy. If it is the valve is opening. Now turn the thermostat off again with someone listening and you should hear a whine / whirr as the valve closes.

 

[ericmark]

You have one boiler, but how many pumps? Had mine been plumbed with one pump it would have been easy, not a clue why two pumps, but that is what causes the problem.

You can have on the S system 10 zones with 10 thermostats and 10 motorised valves as long as only one pump and one boiler all one does is connect all orange wires together.

But with a second pump there is only one micro switch in the motorised valve so unless one add relays you can't have same micro switch power boiler and pump it could be done if the pump and motorised valve power on together, but then the pump is running before valve has had time to open.

I think Stem is likely correct (he usually is) and some thing has failed, most likely is a micro switch.

The way central heating is wired it's easy to get it wrong, with my diagram the domestic hot water relay also works the central heating, NC contact is used when DHW is not required to power boiler for central heating, things like this can cause errors, it did in my case, it's easy to make a mistake.

 

[Edufixer]

Thanks for posts with the help of a friend I have managed to find the loose connection on the switched live buried in the loft between house and annex.
But this still leaves the zoning of the annex. As far as I can work out the annex motorised valve unit only has wiring connected to it and the pump. The micro switch which boiler the orange wire in the mvu is just terminated in the junction box. If I replace the thermostat wheel with digital timer and put in 3 core and e to the mvu will I be able to get the annex stat to fire the heating separate to the main house.