baxi 105e problems

[klee52]

hi, got a strange problem with a baxi 105e, on initial startup on either central heating or dhw, the pump/low pressure light flashes after a few seconds.
the pump prover pin is not extending into the microswitch. when I take the front nut off of the pump, water flows out and then the pin comes out and activates the microswitch and the boiler fires. put the nut back in and all works ok until it gets to temp and switches off, then it follows through the same again. it only seems to run for about 3 minutes and it gets up to temperature very quickly. pump is spinning ok, the only other thing I can think is partially blocked heat exchanger with a weak pump. does anyone have any suggestions??
thankyou in advance.

 

[twgas]

check your system pressure, should be about 1.25bar.

 

[powell30]

If it isn't a blockage or pump issue then you will ned to replace the diverter section (where the pump switch proves.) I would suggest you replace the whole section

 

[DP]

I would be looking for blockage, ripped diaphragm in flow manifold (under pump proving switch) or auto air vent cap not open/ air not being auto purged from the system before embarking major surgery.

 

[klee52]

thanks for all your replys, I recently put some leak seal in the boiler also, sorry I didn't mention this, the pressure is at just over 1 bar so that seems ok but I am now wondering if its the aav that has become blocked because of the leak seal, I may change the pump anyways and also the aav because i have unscrewed the cap on the top and it isnt letting any air out at all. if this fails then the heat exchanger will is coming out, whats the best stuff for cleaning the heat exchanger through? I normally use f5 but im not sure if this will sort it or not.

 

[klee52]

If anybody is interested, I changed the pump and cleaned the aav today, so far, all is working fine.