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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

    AJJewsbury: 
     

    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.

    I thought that the hot water is moved by its own pressure from the potable cold water main though the heat exchanger to the taps, and does not need pumping. 

     

    Please see illustration 2.10.

    Z.

Reply
  • 0

    AJJewsbury: 
     

    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.

    I thought that the hot water is moved by its own pressure from the potable cold water main though the heat exchanger to the taps, and does not need pumping. 

     

    Please see illustration 2.10.

    Z.

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