Hi - this has baffled me and the heating engineer I've called in to look at it. My Baxi 105e has been reporting a fault, the LED indicating it's with the pump or low pressure. However, a quick reset at the mains and all is well again. If there's either a DHW or CH demand, the boiler fires up and I have hot water and rads as normal. BUT - if there isn't a demand, or once the demand has ceased (and the overrun has finished as well in the case of the CH) then the boiler returns to fault mode after about 2 seconds.

The engineer has scratched his head a lot, replaced the PCB (no change) and seems clueless.

Pressure is at about 1.6 bar cold, but over the summer it looks like the boiler was running on low pressure as a result of a leak we hadn't spotted (I've since re-pressurised from filling loop). Pump seems to be fine and is only 3 years old. I'm now wondering whether there could be a problem with the expansion vessel and judging by the dust on the top of the boiler, the engineer hasn't checked it.

Any ideas?

Ta
Mac

Mac, September 2005

Hi my baxi 105e diverter valve was leaking and replaced it with new and now makes clicking noise but does not fire up had plumber round he suggested PCB board is burned PLEASE ADVISE THANKS

ABIDI, July 2015

flame fault showing light 1. can reset then after a few hours flame faultcomes back on.

john boy, March 2012

My 105 he seems to have trouble with the hot water, basically temperature isn't maintained in the bathroom (1st floor) but symptom isn't as far as bad downstairs. I'm guessing it's a pump related problem but the troubleshooting is pointing me to a new PCB. Your thoughts appreciated.

Leigh, December 2010

when i switch the boiler on it flashes 30 degrees ,no heating no hot water,,,help help

john pearce, November 2010

I have had all of these probes an fault codes I have got it down to the venture in the fan/flue system it the part were the rubber tubes of the air pressure switch plug into this part melt an gets deformed allowing the ratios to be wrong this part cost bout 5 quid an has solved my prob.
As for the leak by the air pressure switch it's was the pipe of the bk of the pump which connects with the heat exchanger near the pressure switch there is an internal O ring which I replaced greased up put bk and is now fine

Adam Carey, November 2010

check micro switch in diverta valve spring inside switch might not pushing button back out every time

the board enginer, April 2010

Bart the ans is the venture in the flue one of the hole on the venture is blocked it the 1 wer the 2 clear pipe from air pressure switch

H, April 2010

I had exactly same problem and british replaced 3 parts before finding it was the pump causing fault

2Doorsbob, March 2010

baxi 105e fault led on hwd comes on occassionly

dave, February 2010

my boiler flames up when switched on but goes out after a few seconds

arl, December 2009

Check spindle isnt stuck on C/H flow swith, had an identical fault early this year.

J, December 2007

hot water works,but central heating wont work when called for

janet, November 2007

Just had a fan/flue light flashing on my 105e

primarily checked the flue for blockage (you never know) gave the unit a good clean/vac out
Checked power to Fan when hot water demanded - no output
Still no joy

Ordered replacement PCB - Part No: 5112380 (was 248074)
found this to be an upgraded version - better it seems
off ebay BNIB Item number: 150173291687 for reference price
£48.50 inc P&P

Fitted - (ensure you switch to reset for 3 secs before returning dial to On position) and that power to the unit is isolated - off at fusebox if not on dedicated trip/circuit.
If unsure seek professional help!

Problem Solved
Have my board at work to tinker with and repair for a spare
suspect the Fan relay - but struggling to find schematic details
so will probably replace both suspects!
hope this helps Paul

Paul Hawksworth, October 2007

The pump proving switch spindle (on top of the diverter valve, left hand side of the boiler, not the large one facing you) may be sticking open, from memory the boiler does a check to make sure the switch is closed before beginning an ignition sequence.

Steve BG, August 2007

Bart, what Relay did u find to replace the faulty Fujitsu Takamisawa JV24s-kt ? i have the same fault and don't fancy spending £78 on a new pcb. Cheers Richard

Richard, May 2007

Not an answer but I also have fan/flue fault LED flashing. Im sure its not the fan but the PCB at fault. Can someone please tell me which relay on the PCB causes this fault please?
Thank you.

Bart, February 2007

It seems that the PCB has faulty relays. Baxi changed over to a newer PCB due to the fault, or so I believe. Any how I had a problem with mine. On start up for CH or HW demand the fan starts then shuts of and does this maybe 8 times or so before it lights up, while it does this it indicates a fan/flue fault on led. I asked my brother who is corgi reg to leave the board out while i checked it over. It does apear to have been a relay, i had a lot of trouble trying to find an exact match (Fujitsu Takamisawa JV24s-kt) Any way i found an alternative and connected that up with wires due to footprint being different and now she works a treat. Would not tell my brother how i fixed it when he re installed it but offered my services for repairing them. £1.50 and a bit of wire is a lot cheaper than a new PCB that at some places can cost £100. He did ask what the bit was hanging off with wires though!!!!

Paul, March 2006

No answer, but I've got the same problem. The boiler is less than five years old and the problem first occurred a few days ago. Since then, it's gone wrong and recovered again several times, with the symptoms you describe, except a reset or power cycle doesn't fix mine; It works again when it feels like it. The first engineer said the CH pressure was too low (1 bar), pumped it up to 1.5 and left (to be fair, the boiler was apparently working fine at that point). The second engineer spent an hour or more fiddling with it and concluded that a dodgy PCB could be the only explanation. At this moment in time it's working, but for how long...?

The only suspicious thing I've noticed inside the boiler is a slight leak around the pressure switch that detects the DHW demand; That said, it appears to be very minor and the attached microswitch and nearby PCB housing don't appear to have been compromised.

Having read the above, I'm a little concerned that spending £100+ on a new board may be a waste of money.

Roger Router, January 2006

Sorry this isn't an answer, but I wonder whether you have resolved this problem (having posted back in September)

Reason I ask is that I have exactly the same thing on same boiler at same age.

Andy P, December 2005