Baxi 105e new pcb after flue/fan fault but now rads not hot

Hi there,

We moved into our new house about 6 months ago, it has a Baxi 105e boiler which has worked fine since we moved in, giving hot water and central heating with no problems. We switched the heating on again at the beginning of October and it ran ok for about 3 weeks then came up with a fan/flue error light. We replaced the PCB (with the updated version) and reset it as described. Now the central heating comes on but even with the dials turned up to the max the hot water is still not as hot as it was and the central heating doesn’t get above 50 degrees on the boiler lights and the radiators are only warm to the touch, not hot. There are TRV’s on all the radiators except the bathroom one and we have tried turning a few radiators off and we’ve tried having them all on max. The only other thing we have done is to make sure that the pressure is up to 2 bars, it was down to 1.5, but nothing else has changed with the system so we assume there must be something different about the boards (the original was part no. 248074 and the replacement one was 5112380), are there perhaps some settings on it we could change? The replacement board didn’t come with any instructions.

Thanks for your help!

Firstly make sure you have got the knob spindles in the correct orientation of the variable resistors. Take the pcb cover off and take the kobs out. Then from the cover side use the knob spindle and turn the two variable resistors as far clockwise as they will go, then go back round the front and reinsert the knobs so that they are in their max CH max HW positions.

Failing this it sounds like the new PCB has upset the burner pressures. This can be adjusted but only by a competent person and requires a multimeter, digi barometer or U guage.

Should light at approx 4mbar,@6vdc at the mudureg
Max at approx 12.2mbar @9vdc
Min at approx 2.5mbar @ 1vdc

try your knobs you prob only have half the movement you should have . As bg says, board not positioned correctly

I think I've fixed it. We had already re-aligned the knobs back to zero as suggested when the board was fitted, but when you turn the knobs on the front of the boiler to adjust the heat there is a spot about halfway round that is a bit harder to turn past (it's not an obvious end, just a bit stiffer). We took the front off again and if you use a screw driver to manually turn the adjusters on the pcb itself it is clear that they only do half a turn rather than the full turn that the adjuster knobs on the front do.

I did a quick test this morning and it seemed to be getting up to 60 (wow, 60!!) ok but will check again tonight to see if it's fully resolved. It must be because it's a replacement part it is different, but I think it's really bad that it came with no manual or description of the changes. I won't ever buy a Baxi boiler after this, their technical helpline really didn't help at all and all I've heard is stories of unreliability. Unless you guys have any other advice I've heard Worcester Bosch or Vaillant are the makes to go for?

Thank you for your advice on this, it made me look again at something I thought we'd already ruled out so very glad I posted the question here!