Central heating fault

[Wroot Rhino]

Hello,

My daughter has recently moved house. I am trying to work out what is wrong with the central heating.
The system comprises boiler (Not combi), Pump, indirect cylinder, cylinder stat, motorised valve, programmer room stat and radiators.

I assume this is a pumped system?

The programmer is new because I thought that was the fault as the old programmer central heating light would not come on under any condition.

This is what happens:
Hot water comes on, pump operates, cylinder and radiators heat up, hot water turns off via cylinder stat, pump stops, Radiators cool down!

I can't seem to get the heating to stay on even with the room stat turned up.

The room stat is a Danfoss RMT24 and it does click when you rotate the dial. I can't get the cover off, there are no screws to remove.

Is it likely the room thermostat is at fault?

Any help much appreciated.

Thanks

 

[terryplumb]

Could be a number of things ,testing voltages present at the wiring centre would establish which.
The Motorised valve ,I assume is a 3 port ( MPV) ?
If programmer is set for C/ heating only what is the result ?

 

[Wroot Rhino]

Thanks.
With the programmer set to CH only nothing happens
The valve is a 3 port valve
I have found out the programmer wall plate is Danfoss MK18. there is no wire connected to terminal 2 (CH Off)
The room thermostat might not be RMT 24, it just looks like it!

 

[terryplumb]

Doesn't require a wire to be connected to " central heating off" terminal, the programmer just kills voltage to c/heating " on "terminal ,when c/heating is not required.
What make model 3 port valve do you have ?

 

[Wroot Rhino]

Thanks for your info. I am not at the house and my daughter is out I will find out and post back later. Thanks again

 

[Wroot Rhino]

It may be iflo from memory

 

[ianmcd]

better if you post pics of everything so we know what you actually have

 

[CBW]

Sound like just a stuck 3 port motorised valve. Try setting the hot water for a small timed period and the heating on for a longer timed period, after the hot water is satisfied, see if the heating stays on.

 

[Wroot Rhino]

I will post pictures when I can get to my daughters house.
When the hot water period ends the pump stops therefore the radiators cool down

 

[CBW]

When the hot water period ends the pump stops therefore the radiators cool down

Is that with a heating demand as well?

 

[Wroot Rhino]

Hi Chris,

Yes that is with demand for heat

 

[Wroot Rhino]

Hello,

Pictures as requested.

The broken wallplate for the programmer has been replaced but wiring is identical.

I have tested the stat with a multimeter and when it calls for heat there is 240v on the switched live.

At the control centre, when the wall stat calls for heat there is no voltage on the 3way valve orange wire. The actuator doesn't do anything in any circumstance.

The 3 way valve only moves about 1/8th of a turn is it seized? or is this normal

The central heating pump starts and stops from the cylinder thermostat, when the programmer requests hot water.

 

[terryplumb]

Replace the 3 port valve.

 

[Wroot Rhino]

Hello, Thanks. The complete valve or just the actuator?

 

[terryplumb]

Not much difference in price between just actuator and complete valve. Buy complete valve and you can't go wrong really.