Thermostat not controlling central heating problem

[Teamgoldie]

Hi Everyone,

I would really appreciate some help.

Last year we had a new CH/HW system installed, comprising of

Vaillant ecotec plus 637
ACV smart 210 green
Siemens rwb29 controller
Center honeywell wireless room thermostat.

The HW has been working perfectly throughout and the CH worked brilliantly last winter.....
To control the CH system last year we set the controller to CH manual on and used the programable timer to keep the house at a nice temperature. Turned it to manual off over the summer...

This year when I do exactly the same thing the CH comes on but will not turn off with the thermostat. It is a big boiler, so the house starts to resemble a sauna very quickly.

I have changed the batteries on the thermostat....no better... if you up and down the thermostat it does show the wireless signal on the room thermostat and the receiver box light does go on and off...now is the really odd part...

It was due a service and I explained the problem to the engineer, he was a bit stumped, but as he clicked the vaillant into service mode it started to work perfectly again. put the siemens controller onto CH manual on...The boiler would fire and stop according to the thermostat...worked perfectly for 24 hours, but it has now gone back to the same problem and we are either freezing or in the sauna again

Any suggestions would be greatly appreciated.

Sincerely,
Steven

 

[AGAS]

your diverter valve is fooked probably get away with changing the motor part alone , easy fix .

 

[Teamgoldie]

Thanks for the advice agas

this was a new system with new valves 1 yr ago, the valves are Grasslin, the leads run into a square metal box (im guessing the motor of the valve), would this be covered under a warranty? do they need to drain the system to replace?
isnt it a bit premature to have a fault this quick?

Regards,

Steven

 

[Teamgoldie]

additional info, looking at the valves more closely... there is a lever on the top that says auto or manual open... one valve you can feel resistance as you push this lever and you can feel it moving back into auto, the other one there is no resistance and the lever just flops around.

does this confirm the fault location?

 

[flameport]

does this confirm the fault location?

No, it just means the valve is open.
That could be due to it being mechanically stuck open, or it is receiving power due to a fault elsewhere.

 

[Teamgoldie]

Thanks Flameport,

ok I have been checking the CH valve in various combinations.

without power (CH off on controller and thermostat not activated) the valve returns to the closed position (auto) and the boiler does not fire

with the CH off on controller and the thermostat activated the thermostat receiver unit light comes on but the port valve remains closed and the boiler does not fire...so far so good, i think...

with the CH on and the thermostat on the valve opens (audible whir and lever moves), the boiler fires and the rooms get hot... but switch the thermostat off and the boiler remains on and the valve remains open....hence the sauna....

am I right in thinking this means the valve is functioning mechanically, but is still receiving power to remain open when it shouldn't (as you suggested flameport), suggesting valve replacement will not fix the problem?

does the thermostat operate an electrical switch within the valve actuator that may be ceased closed even though the mechanical valve is still functioning? can I just cut power to the circuit, remove the actuator cover and check for corrosion/switch problem?

I am confused that switching the boiler into service mode made everything work normally. is there a change in the circuit in boiler service mode that can explain this? is there any feedback from the boiler to the port valve?

Thanks again for your help and advice

Steven