Baxi 105e: Pump/low pressure error after replacing diverter and plate heat exchanger

[raidwi]

As per the title - have had persistent issue with hot water running hot for about 20 seconds, then running cold, then running hot again. Central heating has also been doing the same. Radiators would also heat up when running the hot water.

I have drained the system and replaced plate heat exchanger and wet pocket thermostat to deal with the former, and the diverter (it was in a sorry state) with a Baxi original to deal with the latter. Have also ran some cleaner through before draining, and the MagnaClean is picking up very limited junk. Expecting all to now be well I repressurised, bled radiators, then repressurised. Rinse/repeat a few times until the air was gone and set final pressure just above 1 bar.

However now the air has been removed from the radiators, the boiler will not light and I get an error on the pump / low pressure light. Neither central heating nor hot water will work.

I've had the screw from the pump head off and the pump can turn freely, and I can hear it running albeit much more quietly than before. The diverter is activating the microswitches as expected.

Any suggestions on the cause?

 

[gas112]

have you opened the little black air release on top of the pump . also leave screw out middle of pump to get rid of air .

Can be a nuisance to get all the air out sometime constantly turning it on and off will shift it
With boiler off the other micro switch on top of divertor is that in rest position and not touching microswitch

 

[raidwi]

have you opened the little black air release on top of the pump . also leave screw out middle of pump to get rid of air .

Can be a nuisance to get all the air out sometime constantly turning it on and off will shift it
With boiler off the other micro switch on top of divertor is that in rest position and not touching microswitch

I haven't, will try that thank you. But removing the big screw on the pump means a lot of water comes out and the PCB would be in the water's path so I'm being extremely cautious and isolating and draining boiler first before removing the screw so it's only a trickle that my towel can handle. I'm then putting screw back before I repressurise boiler.

Both pins on the diverter are at rest and not touching the microswitch when the boiler is off.

 

[gas112]

do not drain the boiler before removing the big screw do it with boiler pressurised stick a towel under the pump to catch any water no need to let it run once it shows .
the little black bleed doesnt need removed just a turn and a half will do it .
This trick can get the water moving turn your tap on and lift the lever on top of the divertor with an electricians screw driver to activate micro switch this will bring the burner on do it in 10/15 second bursts and it should clear the air

 

[raidwi]

do not drain the boiler before removing the big screw do it with boiler pressurised stick a towel under the pump to catch any water no need to let it run once it shows .
the little black bleed doesnt need removed just a turn and a half will do it .
This trick can get the water moving turn your tap on and lift the lever on top of the divertor with an electricians screw driver to activate micro switch this will bring the burner on do it in 10/15 second bursts and it should clear the air

Weirdly I came to the boiler and it worked without needing to do anything.

However frustratingly the cutting-off issue is still happening.

 

[gas112]

Weirdly I came to the boiler and it worked without needing to do anything.

However frustratingly the cutting-off issue is still happening.

change the sensor in the dry pocket left hand pipe leading to divertor