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Just for information BAXI 105E

whjohnson

Been fault finding on my old combi and having solved the problem I would like to share the solution with those who are still running the old Baxi Water Hotter!

Model of boiler is BAXI 105E combi - Not a condensing combi. This model is around 20 years old.

Nature of fault - No hot water, fan failure fault light on, and flame failure fault light on.

I initially changed the complete diverter valve assembly because the original one was leaking and badly corroded, although this was not actually causing the fault.

I traced the fault to a relay on the pcb which actuates the fan. For information, the relay is marked RL.1

This applies to a Honeywell pcb with the following markings printed on it -

CE 00518L 1810

CS0118E-LS

TYPE:MIDINT00

CD 995099 2

CD 565599 2 

I sourced a replacement relay from ebay, in fact I bought 2, since there are 2 identical relays on the pcb so I got a spare.

Relay part no details - 

TAKAMISAWA JV24S-KT

5A 30VDC

250VAC

SPST

Coil voltage is 30VDC, cantact voltage rating is 250VAC

I unsoldered the original relay and connected 30VDC across the coil and a multi-meter set to ohms across the contacts - result was open circuit.

I repeated the process with the new relay and got continuity across the contacts and a satisfactory click as the coil energised.

I had a spare pcb but that didn't work at all when I just did a straight swap. Anyway I hope someone finds this info useful.

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  • 0

    What alters in the boiler when the room 'stat is satisfied to stop heating the rads?

    In principle that microswitch on the diaphragm valve switches the gas & pump between the room stat/clock control and definitely on (when there's DHW demand).

    (In practice it's a bit more complicated as the whole sequence will be overseen by the PCB - first starting the flue fan, then checking by an air pressure switch that it's working, then starting the pump, then opening the gas valve a little, firing the ignition, checking that a flame has been created, then fully opening the gas valve and so on, at each stage possibly aborting if things don't go smoothly. Likewise on shutdown it'll probably keep the fan flue running for a short while to clear the combustion gasses and then the pump for a bit longer to stop the primary heat exchanger from kettling.)

       - Andy.

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  • 0

    What alters in the boiler when the room 'stat is satisfied to stop heating the rads?

    In principle that microswitch on the diaphragm valve switches the gas & pump between the room stat/clock control and definitely on (when there's DHW demand).

    (In practice it's a bit more complicated as the whole sequence will be overseen by the PCB - first starting the flue fan, then checking by an air pressure switch that it's working, then starting the pump, then opening the gas valve a little, firing the ignition, checking that a flame has been created, then fully opening the gas valve and so on, at each stage possibly aborting if things don't go smoothly. Likewise on shutdown it'll probably keep the fan flue running for a short while to clear the combustion gasses and then the pump for a bit longer to stop the primary heat exchanger from kettling.)

       - Andy.

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