DHW no heating - S.10 code - Vaillant Ecotec Plus 831

[zevans23]

Hello guys, had a bit of a search around on here but can't find this exact problem...

I think this code S.10 means the boiler thinks there is demand for hot water. The problem is that it's showing this code all the time even when hot water taps are closed so it never sends heat to the radiators.

I'm fairly sure there are no leaks in the DHW pipework - I have checked where I can see and there's no damp patches or damp smells anywhere so I don't think there can be a leak under the floorboards. (House is frequently empty for several days running at the moment)

I read in a post on here (which I can't find again, grrr) to turn off the cold water feed at the isolation valve and see if the heating eventually comes on - so I'm trying that at the moment, but
- what else can I do to identify the problem for sure
- what else can I try to fix it?

Hot water works fine and the heating works intermittently so I know there's not a fundamental problem with it. I've run all three HW taps at once and switched them off lowest first to try and make sure there's no air.

Just realised I didn't include the shower in that, something else to try!

Help!

 

[MANDATE]

My thoughts are you may well have a fully pumped system.
You may have two 2 port valves one for HW and one for CH or you may have one 3 port valve which moves to one of three positions ie HW or HW/CH or CH.
Usual problems with a 3 port are
faulty motor so it basically stays at the rest position which is HW.
Sometimes motor is OK and valve will move to mid position but no further.
This being due to either faulty micro switch in the valve head or no power on the grey wire to drive motor forward from mid position.
Sometimes the valve does move correctly to CH position but a second micro switch being faulty does not allow power to come from the valves orange wire to light boiler.
If you don't have a fully pumped system then I would think the circulating pump is the most likely at fault.
Or if your boiler is a combi then most likely the diverter valve which controls the HW and CH is sticking.
So what system have you got?

 

[Netdragon]

probably a tap dripping somewhere that can trick some boilers to fire up or the dhw flow sensor is broken and thinking there is a demand and cycling the boiler on that.

As to test and work on the sensor in question requires the combustion chamber casing removal get a RGI to visit it be a simple fix and a part. Short of turning of all taps.

If the appliance is under two years you may have a valid warranty on it still and they may visit to repair.

Can also consult the manual for the D22 i think its that one to see if HW demand functions (diagnostic menu options)

 

[stardanny]

My thoughts are you may well have a fully pumped system.
You may have two 2 port valves one for HW and one for CH or you may have one 3 port valve which moves to one of three positions ie HW or HW/CH or CH.
Usual problems with a 3 port are
faulty motor so it basically stays at the rest position which is HW.
Sometimes motor is OK and valve will move to mid position but no further.
This being due to either faulty micro switch in the valve head or no power on the grey wire to drive motor forward from mid position.
Sometimes the valve does move correctly to CH position but a second micro switch being faulty does not allow power to come from the valves orange wire to light boiler.
If you don't have a fully pumped system then I would think the circulating pump is the most likely at fault.
Or if your boiler is a combi then most likely the diverter valve which controls the HW and CH is sticking.
So what system have you got?

831 is a combi.

Zevans, switch off heating and turn off cold feed to combi, then is DHW still demanding? If it is, flow sensor faulty.
You need a Gas reg engineer to replace it.

Dan.

 

[zevans23]

So I left heating and boiler off for a couple of hours, with the cold feed switched off. When I switched back on I had heating for a while and then the next cycle, after the radiators cooled enough to trigger it, went back to the same old problem.

Zevans, switch off heating and turn off cold feed to combi, then is DHW still demanding? If it is, flow sensor faulty.

Arrrgh. Yes. Time to call him I guess - I'll see if I can figure out that D22 thing though.

 

[zevans23]

I think I must have a tiny leak somewhere upsetting it.

I had the problem again but NEEDED heating so left the DHW feed off and turned the boiler off too for a while.

I then turned the DHW inlet back on HALFWAY - in the interests of science - and the heating's been happy ever since, and using hot water fine. Obviously DHW flow has dropped a bit but it works on demand and it's still just enough for the shower.

Does this mean there's a tiny leak somewhere that isn't triggered because I've throttled the water? Or does it mean the mains pressure might be too high and that's causing a problem and I should turn the main stopcock down? Or is it all evidence of a flaky DHW flow sensor?

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