Vaillant ecotec plus 630: pump overrun/no hot water

8 Feb 2015
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United Kingdom
Hi all

Moved into new house on Friday; system initially seemed to work ok, but then today there's suddenly no hot water. Setup (pictured):

Vaillant ecotec plus 630 boiler
Honeywell ST6400 heating programmer
Ariston water storage cylinder

Water runs but isn't hot (isn't totally cold either, but far from even lukewarm). Display occasionally reads S.7 (i.e. 'pump overrun'). The rest of the time it reads S.31 (I.e. 'summer mode'). The boiler may have been switched off and we may have been using the cylinder contents over the past two days?

Any help much appreciated!


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you will either have either 2 x 2 port motorised valves or 1 x 3 port motorised valve somewhere, locate these and post a pic of what you have
Thanks for your reply. Pic attached of what I found...


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Great well for future reference you Hav a fully pumped S plan system, those valves have small motors in them, when powered by your programmer , and if the corresponding thermostat is calling for heat, the motor opens the valve to allow hot water to flow, once the valve is open it sends an electrical signal to the boiler to come on, there is a small lever on the end of each valve one should show resistance when you try to push into the manual position and one should move freely with the HW only selected , is this the case ?
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Thanks, this is really helpful!

Yes: the lever on the top valve (which feels warm to the touch), moves freely between auto and manual.

The lever on the bottom valve (which feels like room temperature), seems to 'stop' half way, when I try to move it to the manual setting.
Then the valve is working but it seems that it is not making the end switch to signal the boiler to fire, the valve that moves freely is the HW one, turn the CH thermostat dial on the boiler up and any room thermostat that you have up also, then turn the CH on at the programmer, the other valve should now open and the boiler should come on, if it does go back to the HW valve and see if you can feel the pipes either side of it getting hot
CH thermostat on boiler turned up
Room thermostat turned up
CH on at the programmer

And yes, pipes either side of the HW valve are hot to the touch!

Should I try the hot water yet?


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OK seems like you have a faulty micro switch in the HW zone valve, if you have TRVs on your radiators go round and turn them all off and leave that set up for an hour and you will have a full tank of HW and then you can switch the heating off again, you can do this until you can get a replacement actuator head fitted to the HW zone valve, no need to drain anything down, your valves have removable heads
Thanks, this is super helpful! One issue: we've got underfloor heating in one room - is there an equivalent of a trv for that? Unsure how I'd turn it off...

Oh, and should I turn the trv's on both sides of rad down?
You wont get HW instantly you will have to give the Cylinder time to heat up, the UFH should have a seperate thermostat just turn that down, no need to close both sides of the rads just close the TRV s
Many many thanks. Most of the old flimsy trv's are too broke or the little metal rad valves are too stiff, to turn them off. I'll deal with a hot house, until I get a replacement actuator head!
Thanks again for this. Quick update: replacement brought and fitted. Everything now working ok! :)

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