Heating Controls - CH not working without HW

[D R Thompson]

Hi,

I have a problem where the CH only works when the HW is on!!!!

I have changed the system programmer from a Danfloss CP715 (fitted in 1999) to a Danfloss FP715Si thinking the programmer was at fault - still have the problem.

The system is pumped with motorised valves on both CH & HW, both motorised valves appear to be operating OK and open / close as I would expect.

Any advise would be very much appreciated.

Regards DRTGET

 

[45yearsagasman]

My guess is that the micro switch in the CH valve is not closing even though the valve itself opening. That is assuming you have no other wiring errors after changing your programmer. A simple check using a multimeter will confirm.

 

[stem]

Inside the head of each motorised valve is a small microswitch that operates when the valve is fully open and starts up the boiler. It sounds to me as if the valve is opening, but the microswitch has failed, so the boiler doesn't start. When the hot water comes on, the hot water valve operates the microswitch in its motorised valve and starts up the boiler. At this point, because the motorised valve for the heating is open the radiators heat up too.

It's quite easy to check if you are reasonably competent with electrics. Remove the central heating motorised valve orange and grey wires from where they are terminated (note carefully where they came from so that you can put them back) then with a mulitmeter measure the resistance across them with the heating on and off. When the heating is 'on' there should be zero resistance measured between the two wires.

 

[D R Thompson]

Hi Retired, trust you're enjoying retirement like me, but have to keep our hands in!!!! (I'm a retired Mech' engineer)

Many thanks for the advise, I assume changing the CH motorised valve is needed or can the micro switch be replaced in isolation?

Regards DRTGET

 

[ianmcd]

some motorised valves you can just change the actuator head with no need to drain the system , if you post a pic of the valve we will be able to tell you if the head is removable
, also note if you are testing the micro switch make sure the mains supply is isolated and as one of those wires is a permanent live

 

[D R Thompson]

Hi Ian,

Photos requested, sorry about the quality, valve in a tight spot (as usual!!!!!)

Cheers

Dave

 

[45yearsagasman]

Those heads can be replaced quite easily. I never bothered replacing the micro switch. Too much of a faff.

 

[D R Thompson]

That's great news, many many thanks for speedy response and advice, it's very much appreciated.

Regards

Dave

 

[GeoffH]

Hello, I have the same 'intermittent' problem.
I googled for a solution a few weeks ago, before this thread started.

A reason that I found was that the valve may not be fully opening and so not operating the micro-switch.
I think that this is my problem, as once the CH water is hot enough, the valve manages to operate fine between room stat cycles.
When starting from cold, I have to program the HW to come on at the same time.

When spring arrives, I need to decide on a new valve (need to drain down as no gate valves either side of the zone valve), or a replacement head.

 

[oilboffin]

Either way change the top.Bob