Baxi 105E

[DP]

Fitted this boiler a few years back as a plan S with boiler supplying hot water in the kitchen and shower. Bathroom hot feed is from cylinder.

House was extended by a builder. Extention has underfloor heating.

While the original S plan MV auxillary switches applied clean loop across boiler '3 and 4' to start boiler, builder's plumber used the third MV auxillary switch to apply 240 volts to the boiler (in effect boiler was live when switched off at boiler front panel).

PCB had to be changed as the fan would 'kick' but not run a few months later.

Soon the boiler started to fail with the new PCB. The failure indication now was 30 degree light flashing with boiler locked out. Reset would restart the boiler sequence. The 30 degree LED started to flash as soon as the pump was powered up by the PCB. Baxi adviced a replacement PCB. This was done but same thing is happening again couple of month later.

Can Potty pros assist repairs as the client is a gentleman and a good friend. Email in profile.

 

[Agile]

That does not sound correct to me but how has the third MV been connected to "supply 240 to the boiler" ?

Perhaps I am missing something but why was it not also connected across 3 and 4 like the others?

Having said that the PCBs on these boilers are not the most reliable although many are changed when OK as a result of a misdiagnosis of a gas valve setting fault or even a flame detection electrode positioning problem.

Tony

 

[namsag]

Not the cleveriest of thing to do having a boiler still live when switch says off.. By 3 an 4 . you mean 1 an 2 as there is no 3/4 on connector strip. Personally would wire it correctly to make sure this was not affecting the board in any way can`t see how it could but would take any doubts away

 

[DP]

That was done before the PCB was replaced. Now, each motorised valve aux switch effectively links 1 and 2 (not 3 and 4 as I wrote).

The underfloor heating wiring was carried out by builder's electrician. Difficulty is, the spark may not understand what the boiler needs. One has to know what the boiler requires and wire accordingly.

I went to great lenth to plumb the S plan so as not to have nuisance circulation to radiators during HOT water heating cycle. The builder's plumber comes along and relocates the tee offs. Now, during UF heating run cycle, radiators zone that is not on call, heats up.

 

[ChrisR]

Check the APS is connecting the NC contacts properly (black and brown, from memory).
If you put a 20kR/V meter across it the boiler might spring into life..

(A Potty man once told me Performa boards are "damaged" if live is maintained on stat conns when the boiler's switched off.)