Hot water but central heating only works in the mornings .

[The831Bunny]

Servo valve is not returning 100% after hot water use. It's had all night to settle when heating works first thing in the morning. As soon as you use hot water it may not return correctly again. Test for 230V AC on T4 in boiler control box with clock on, if confirmed you can forget external controls. If the arm of the servo valve is sticking, then replace it.

Any boiler must be serviced regulary but with an open flued boiler it is a MUST! These appliances require an engineer experienced in dealing with older Vaillant's. Find yourself a GS registered boiler engineer to take a look. With some TLC this model is very robust. If you haven't already, I'd strongly recommend a CO alarm with any open flue appliance too.

 

[emin-j]

Thanks for your help guys strangely enough the heating has been working fine for days
However, my Daughter turned the hot tap on in the bathroom last night and the water was Brown ! it lasted for about 10 seconds then ran clear and has not happened since.We have had Brown water from the cold tap but that was when the mains in the road was being repaired some time ago, any idea what this could be ?