URGENT Baxi Duo-Tec Combi 33 HE DHW Fault

[PensivePenguin]

Hello,
Looking for someone who can please help solve this problem and fix our boiler.
Staffs area.


CH seems fine. Boiler can be coaxed into full burn with the fan spinning at full speed, so I think everythings fine on the gas/air/flue/condensate side of things.

If there is DHW demand on the boiler, the hall effect sensors comes on (red neon lights up) and the green DHW LED comes on. The pump runs and either:

• The boiler ignites but the boiler doesn't reach more than ~33° and the water is tepid at best
• The boiler refuses to ignite at all

If the boiler is hot from CH demand, it either quickly cools down with DHW demand until it reaches ~20° and then ignites but doesn't go full flame and the fan doesn't spin at full speed. It struggles to reach and maintain a temperature in the thirties. Less often, it doesn't ignite at all.

 

[PensivePenguin]

(cont'd)
The 3-way/diverter valve seems to be working. If I let everything cool down and then demand DHW, the CH outlet and return stay cool. I'm guessing it's safe to say, that the heat exchanger plate is in good order as the boiler cools down so quickly when switching from CH to DHW. (We can get hot water for a few seconds this way, which I guess is the residual CH heat being drawn off the boiler)

I've check resistance of DHW temperature sensor and that seems, as far as I can tell, pretty much bang on spec. There are no fault codes.

Last week condensate pipe froze up. There was a blockage at the end (organic material from the gutter it's drained into) which I think contributed. The boiler was, from time-to-time alerting E133. I removed the condensate pipe and drained the boiler into a bucket. It worked well enough after that for us both to take hot showers. I've since replaced the condensate pipe, and this DHW situation started. I can hear water trickling down into the condensate pipe with CH demand so I'm confident that's all working as it should be and there's no blockage in the trap.

 

[PensivePenguin]

(cont'd)
Anyway, fairly keen for someone to help us out with this. Not looking for it be sorted on the cheap; I've had no joy making enquiries today - must be something to do with all the cold weather we've had.

Thanks