Vaillant ecoTEC plus 831 heating not staying onthe temperatu

[Libstick29]

hi, we have an ecoTEC plus 831 and we’ve had issues with the heating staying on. When we came back from holiday the water pressure was low and I fixed this. The digital radio thermostat (Salus model RT300RF) was also out of batteries and we replaced these. No settings were changed. The heating worked okay we think but we were just home for a night. We went away again for a few days and switched boiler off. When we came back the heating came on and worked fine but then after about 3-4mins it turns off. Then we get status S.7 (pump overrun) and finally S.30 (room thermostat 3/4 no heating demand). After it has cooled down it turns back on again for a few minutes but never to the desired temperature on the external control. We have reset external thermostat but the behaviour is the same. Right now we have the boiler radiator temperature control set to 65o. The thermostat is set to 23o. The boiler display says 38o and its currently cooling down. Earlier today I did move D.0 from the previous setting of 24 down to 10. I’ve no idea if this was a good or bad thing to do but the behaviour of the boiler is the same since doing that though radiators are getting a bit hotter.

Sorry if I haven’t given enough info of the boiler etc, let me know what else you might need to know and I will try or if I should reset D.0 back to previous setting.

I have included photo of controls. Boiler is on in photo but cut out at 49o and the display now says 38o. I think it goes back on when it gets to 36o. Digital thermometer currently reads 16o

Thanks

 

[transam]

u may be best advised to post this in the plumbing and heating forum

 

[SammyInnit]

A lot of suggestions for this boiler and similar issues suggest a flow problem. How old is the system? My first thoughts would be thermostat, even with new batteries they can just be not working properly at all. Next would be flow, diverter valve and heat exchanger.

 

[Libstick29]

Thanks Sammyinnit, the system predates our purchase of the house but I think it’s about 2009. I thought it might be the thermostat too but not sure how to check that or try to bypass the external thermostat to make sure.

 

[SammyInnit]

Easiest way to check the thermostat is shut off the mains electricity to the boiler completely, where ever the base point of your wireless thermostat is will have a relay switch, basically a send and return wire that will create a circuit to tell the boiler there's a call for heat. You need to manually close that circuit. If it fixes the problem then it's the thermostat.