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AllyBongo

Plumbers Arms member
Plumber
Gas Engineer
Dec 9, 2010
499
45
28
Scotland
Member Type
Heating Engineer (Has GSR)
Got a fresh batch of gas certs/services to do for a new landlord, 1st one I go to has a Baxi 105e, tenants shows me that the gas hob goes out when the boiler fires up! Turned out the gas valve handle was off and the valve was just cracked open, this boiler was seemingly serviced by BG in August!!

Anyway, opened the valve and the working pressure was fine, however the boiler was having some issues. On hw the temp was ramping up the burner was cutting out. High bp was 12mb, so a tad low. Got the low bp to 1.8mb. Suspected pex, but when i turned the hw stat down the gas valve did not modulate, even right at the lowest setting. Flow rate wasn't as high as it should be, but not worryingly low. On heating it fired on low burner then slowly ramped up, so I assume the gas valve is ok.

Didn't want to spend much time at it, as with the overall condition of the boiler it could be a replacement job. But will be speaking to the landlord tomorrow to see if he wants it diagnosed and repaired or down the new boiler route. Any common issues with these, I remember another one a while ago that we ended up replacing wouldn't go to low burner with one of the black wires removed from the mod coil, slightly different, but always annoyed me what was causing that too...
 
Blocked plate it sounds like.

These boilers stay at high rate for ages before modulating down, but might be worth checking the resistance of the thermistor
 
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Really? Do they always fire on full burner? Even if the hw stat is at its lowest setting?
 

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