Vaillant ecotec plus 624 does not stop firing / heating

[Uwe]

Hallo, I have above boiler since around 3 1/2 years with two Honeywell CM707 thermostats, one for upstairs and one for downstairs. Worked brilliantly for 2 years and still does the job in summer for hot water, but now as soon as heating season comes, boiler often stays on and fires no end without following the programmed cycles from the thermostats. Sometimes it works, sometimes not.
Those times when it keeps firing, thermostats themselves show on display the right status , I.e. Off - but the boiler display shows the radiator symbol, burner operation symbol, internal pump running and activated gas valve.
very grateful for help ?!

 

[D_Hailsham]

Probably a problem with one of the motorized valves.

View media item 11762
Turn the power off.

Check each valve in turn, as follows:

Move the lever along the slot from Auto to Man, then release

There should be resistance when you move it and it should go back, by itself, to Auto.

If the lever is loose and doesn't return, the valve is sticking open.

 

[Uwe]

I found 3 motorised valves: one for hot water, one for upstairs and one for downstairs heating.
Actually two (cringe smile) do not seem to work correctly, the hot water and downstairs heating one. They are Honeywell F 3 - 9647 valves.

So your likely diagnosis was not only prompt but also correct!

 

[Uwe]

By the way - I opened the box and sprayed some rust loosening, thin oil in the middle. The hot water valve immediately moved very easily. The stuck heating one improved but does need replacement, however it also currently works. I feel it will last until the plumber has time.