strange problem with 105e

[diverdee]

hi
strange problem with 105e.fixed hundreds of these boilers n never had this one hope someone can help.

boiler sits fine in standby but when you request either dhw or heating pumps cycles off and on 5 or 6 times then fan starts and fires but the indicator light for dhw or heating does not come on till pump has tried say 6 or 7 times.pumps runs for 2 seconds at a time have checked both flow switches and wiring and they make straight away all thermistors in range tried second hand pcb n it does exactly the same and it does the same cycle every time boiler gets to temp or is shut down and restarted.

have tried all the usual process of diagnostics and nothing i find it strange there is no demand light straight away and fan wont run till pump has cycled even though the flow switch has made and the voltage is there.



and is definitely the right pcb!! any suggestions anybody regards david

 

[picasso]

pump capacitor breaking down ?

 

[matt1e]

Wiring loom/connector problem at a guess, how Rhythmic is the cycling of the pump? I know you said every 2 seconds but is it that steady or is it more sporadic than that?

Matt

 

[diverdee]

hi tnx for replys

no am sure its not pump cap breaking down because it always fires first time if you switch off at wall it only goes faulty at second firing.checked all harness for continuity and all tests fine .has me bamboozald.the bit i cant understand is why the green demand lights dont come on till later on in the cycle.

the pump is very regular with its cycle of off and on. it is not spasmodic

 

[Agile]

Have you actually measured the contact resistance of the pump proving switch?

Or even easier measured the voltage across it in circuit as it operates?

Or less technical to short it out at the point when it would operate. Not the recommended way though!

 

[diverdee]

have taken the 2 wires off and linked with wire as pump starts and yep voltage is fine. am a sparky not plumber so these are the easy parts to test for me

 

[diverdee]

but even if this was the case demand lights would still show!!

 

[diverdee]

when u open a hot tap the green indicator light comes on after about 40 seconds.even though the differential microswitch has closed and proved

 

[Agile]

I expect its actually something very simple!

But without being there and seeing it myself I cannot guess!

 

[diverdee]

its doing my head in.hate it when u get one and no matter what you try u get no further forward.its gotta be electronic not a mechanical failure but what lol !!

 

[diverdee]

its almost like the boiler is doing a purge but as we know that boiler does not