baxi combi 105 e,no domestic hot water

[rhubarb44]

Any help please ; as plumber who attended is so far baffled!
boiler works ok on central heating but flame cuts out as soon as hot water is drawn.seal on diaphragm seemed ok but replaced just in case.
heat exchanger cleaned through in case of any muck etc .no joy
will come on occasionaly but soon cuts out

 

[bengasman]

When does it come on, and when doesn't it?
Without more info, the list of what it could be is pretty long.
When did it start? Any other problems now or in the past?
History of boiler? How often has it been serviced?

 

[ollski]

I'll ask a pal tomorrow we had one in the area exactly the same, I think it was something sticking in the main valve body but I wasn't paying too much attention at the time.

 

[namsag]

Heat ex ,,,, you mean the plate heat ex how did you clean it

 

[rhubarb44]

thank you,
when central heating on the boiler is firing ok.open up any hot water tap and the flame shuts off.Boiler installed March 2007 no problems excepting aprox 6 months ago for a few days boiler did not come on a couple of times then seemed to remedy itself.no service history since installation.
Visiting plumber removed heat exchanger and flushed with waterunder pressure and also piping to pump etc in case of "crap" in system but he said it appeared clear.

 

[gaspro1981]

get him to check the operation of the primary flow switch when trying to demand dhw if the pin is not making the micro switches then it will certainly be a blockage in the plate he

 

[ollski]

Aparantly it was the pin sticking in the primary flow switch, not the visible one the one behind and the boiler was just heating the bypass on hw demand.

 

[Agile]

If a plate HE is partially blocked it will do little to just flush through under presure. It needs chemicals to dissolve the debris.

If you run a hot tap and LEAVE it running then what happens next ? Does the burner come on again after a few minutes?

Have you got TRVs on all your rads or have you turned rads off?

Tony

 

[rhubarb44]

problem was|is with the hot tap on th burner would go out withwin seconds and not come on again no matter how long left running
trv on all rads excepting bathroom.My recollection said one had to be permenantely on as a safety overide?
At the moment the boiler seems to be behaving itself!.The only action i have taken is to open adistant Rad to confirm heating ok.They have not been active of course because of hot weather.Can this have had any effect?

 

[baxpoti]

Have had this before and after a lot of head scratching ended up changing PCB, haven't been back since, as far as I know.

Might pay to disconnect and reconnect all PCB connections.