Google is your friend! 0b Burner blocked No flow of water through boiler / reverse flow / Air in heat exchanger Check:- pump operation / direction, flow and return connections are the right way round, for blockages, that system valves are fully open, the heat exchanger is fully vented).
Hi Craig, working with Viessmann Tech they suggested cleaning exchange plate, so we replaced, whilst i was in there i noticed diverter valve was stuck slightly open, so replaced....same fault. Had heat exchanger out & soaked in hot caustic over a weekend, replaced pump head & HW flow switch....same fault. They said new pcb, replaced !....same fault ! Removed hydraulic block from diverter valve, cleaned & off it went. Left customer happy & 2 days later same fault ! Got good CH flow now, flushed system & fitted a TF1 as it was really bad so don't really know where to go now ??????
Sounds like it was / is very dirty inside. It may be a blocked pipe inside the boiler that is causing the problem, and after you clean it out, a few days later it's just sludged up again. As Kiab sad there can't be much left and at the cost of those parts and your time, it might have been cheaper fitting a new boiler. Might be better to give it a good long flush with some pre added chemicals, possibly remove the rads too and clean them out properly
Might pay to, leave some system cleaner in for a few days, then throughly flush through. Put, some Sentinel X400 in my system here, left it in for two weeks, thet recommend up to 4 weeks, flushed through twice, yet last week I drained system down again to add another radiator & the crud that came out surprised me, I can only think it got stuck somewhere.
The saga goes on !....this afternoon Viessmann have said as the boiler is mounted in the attic of this house & this model is a pre top vented type that they are sure air pockets are passing over a flow switch in the outlet pipe beneath the heat exchanger? They are very sensitive & once a signal has been sent to the pcb it won't reset & has to be powered down. So ive got everything crossed for tommorow !
I'm always a sucker for a charity case !.....& they always seem to come back & bite me ! Viessmann were so confident it was all going to work when i changed the first couple of bits!..should have just thrown the thing away! If the switch doesn't work they reakon the looms faulty !!
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