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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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    I suspect a faulty relay with welded contacts that keeps the central heating pump running even when the control knob only calls for hot water.

    With most combis it's usual to have a single pump that's used for both CH and hot water - when hot water is called for a diverter valve changes the flow from the pump away from the radiators to an internal heat exchanger that then heats the hot water - the hot water (DHW) isn't directly heated by the gas burner. There's a whole chain of events that needs to go right for correct operation - a pump running continuously could just as easily be caused by a stuck microswitch that detects hot water flow (usually on the diaphram valve) or a faulty overrun timer.

       - Andy.

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  • 0

    I suspect a faulty relay with welded contacts that keeps the central heating pump running even when the control knob only calls for hot water.

    With most combis it's usual to have a single pump that's used for both CH and hot water - when hot water is called for a diverter valve changes the flow from the pump away from the radiators to an internal heat exchanger that then heats the hot water - the hot water (DHW) isn't directly heated by the gas burner. There's a whole chain of events that needs to go right for correct operation - a pump running continuously could just as easily be caused by a stuck microswitch that detects hot water flow (usually on the diaphram valve) or a faulty overrun timer.

       - Andy.

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