Baxi 105

[doitall]

I have a baxi 105E. It has developed a fault in that when you demand hot water the boiler will light and the water heats nicely. When it gets to about 40 degrees the flame shuts down and when the water cools it light up again and just cycles like this continuously. There are no fault lights showing. My plumber has changed the PCB, changed the hot water and heating sensors, changed the air pressure switch and cleaned the secondary heat exchanger. If you turn down the heat nob for hot water on the front panel the flame will stay lit but the water is cool so it sounds heat related. Any ideas

Posted on another forum, anyone got any clues.

Primary HX is clear, and he has changed all the sensors,

 

[bripl]

filter on the ret below the pump could be full,isolate valve drain boiler and remove filter check and clean,just a suggestion

 

[corgiman]

filter on the ret below the pump could be full,isolate valve drain boiler and remove filter check and clean,just a suggestion

A suggestion that nine times out of ten is on the button

 

[Agile]

Sometimes the filter is wrongly fitted on the flow instead!

I see this on about 40% of this model.

HOWEVER that will not affect the hot water delivery.

The fault is probably with the gas valve setting and needs a CORGI to check and reset it properly!

Tony

 

[corgiman]

Sometimes the filter is wrongly fitted on the flow instead!

I see this on about 40% of this model.

Tony

Thats true, in fact I had one like that the other day

the DHW HE was clogged to breakfast time

Installers Eh?? tut tut tut

 

[doitall]

Thank you kind Sirs

I have posted your suggestion.

 

[Agile]

This "plumber" is probably incompetent as he cannot find the fault and just changes parts.

If this is one with a DRY pocket on the sensor then he probably did not fill it with heat sink compound before replacing. That will give a delayed thermal response.

Tony

 

[doitall]

This "plumber" is probably incompetent as he cannot find the fault and just changes parts.

If this is one with a DRY pocket on the sensor then he probably did not fill it with heat sink compound before replacing. That will give a delayed thermal response.

Tony

You are probably very right Tony

I have tried it at 40 degrees but it does exactly the same as if its set on maximum temperature. The bloke who is looking at it turned the gas pressure down manually today as an experiment and the flame stayed lit but the water was only warm. Please note the full gas pressure is correct as per the manual. Does that give you any clues. The primary heat exchanger was checked clear as well.

 

[bripl]

agile wrote
HOWEVER that will not affect the hot water delivery
very true tony

agile wrote
The fault is probably with the gas valve setting and needs a CORGI to check and reset it properly!

again tony you are correct but as the pcb has been changed and the thermistors i would of thought the gas valve and settings would of been checked then as the boiler was recommissioned poor hot water performance first thing i check is burner pressure and correct modulation as any self respecting rgi would do

 

[Agile]

again tony you are correct but as the pcb has been changed and the thermistors i would of thought the gas valve and settings would of been checked then as the boiler was recommissioned poor hot water performance first thing i check is burner pressure and correct modulation as any self respecting rgi would do

Thats what we do but clearly this fellow is not competent ( as he cannot find the fault ) and one cannot expect that he has done these basic checks.

My expectation is that the MINIMUM gas pressure has not been checked/set. Few RGIs seem to be able to do that.

If that was cprrect then there may be a delayed thermal response re. sensors.

Tony

 

[baxpoti]

if all above correct, plate heat ex needs replacing.

 

[ChrisR]

Temp probe, £20, would find it pretty quickly