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Just for information BAXI 105E

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.

Parents

0 mapj1 over 3 years ago

being a nosey git, I would love to learn how the gas valve is modulated. I assume there is a sensor and a chip involved.
well, there always is a chip or 2 these days. Actually a lot of the modulation in modern boiler is really done by a changing the fan speed of the air, and one or 2 gas jets are then solenoid bang bang control but the varying airflow means the gas jet or jets is/are poking into a variable degree of vacuum so more or less gas is sucked out depending on the airspeed. This is not unlike the petrol uptake from the jets in a carburettor varying as the throttle opens, and with care mixture can then be optimised over quite a wide range. - I assume you remember adjusting cars with those.
Truly modulating gas valves are rather rarer in a domestic boiler, but behave like little more than a motorised gas tap Internally usually either a needle or butterfly valve with a closed loop feed back from a position sensor and a servo loop to compare the degree of valve opening with a control voltage or pulse-width modulated stream. Unless it has changed recently, remote control plane actuator servos work on the same lines.
Mike.
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0 mapj1 over 3 years ago

being a nosey git, I would love to learn how the gas valve is modulated. I assume there is a sensor and a chip involved.
well, there always is a chip or 2 these days. Actually a lot of the modulation in modern boiler is really done by a changing the fan speed of the air, and one or 2 gas jets are then solenoid bang bang control but the varying airflow means the gas jet or jets is/are poking into a variable degree of vacuum so more or less gas is sucked out depending on the airspeed. This is not unlike the petrol uptake from the jets in a carburettor varying as the throttle opens, and with care mixture can then be optimised over quite a wide range. - I assume you remember adjusting cars with those.
Truly modulating gas valves are rather rarer in a domestic boiler, but behave like little more than a motorised gas tap Internally usually either a needle or butterfly valve with a closed loop feed back from a position sensor and a servo loop to compare the degree of valve opening with a control voltage or pulse-width modulated stream. Unless it has changed recently, remote control plane actuator servos work on the same lines.
Mike.
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Just for information BAXI 105E

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