Boiler repair gone wrong

[duffy78]

Right,

have spoken to the plumber. This is how i understand the situation. The switched live in the terminal block is not switching, this is not giving the call for heat. He has said even with a permanent live connected into it. it is still not giving a call for heat.

He says that he spoke with one of the boiler manufacturer technicians to try and determine why the above was and they narrowed it down to the wiring loom.

He says if i can get a wiring loom made then thats prob the best option, if this works i have offered to pay for his second call out and if it doesnt then we'll go ahead with the boiler replacement.

The problem he thinks is two wires touching along there length and that my testing for continuity with the wires in situ would give a false reading as there are parts in the circuit which complete the circuit and give a positive reading.

The part of the loom he is questioning is the one going to the fan, so what i am going to do this afternoon is disconnect either ends of this part of the loom and check for continuity and also for any cross talk between wires.

does this seem like a reasonable thing to do?

I have also just ordered a recondition pcb just to give that a try, it was cheap so hopefully it isnt dodgy!

Now that he has told my where the fault in the circuit is i think i may be able to narrow it down some more, he seems to have been thorough in his testing but was only interested in a like for like replacement of the loom with an off the shelf item so thanks to those who offered up getting a new loom made, thinking out of the box according to him.

 

[duffy78]

Myson appolo is not 15 years old try 25 plus came out around 1980.
Although a lot of parts are the same as thorn apollo they have a different PCB so be careful if it requires ordering,


What exactly is the boiler doing what stage does it get to NOW

Fan running then sparking and attempting to ignite
or
fan running and no ignition spark

ok, ive got the part number off the pcb, it was superceded by another pcb so thats what ive hopefully got.

namsag,

When the programmer calls for heat the pump starts up, the divertor valve switches across to whatever is required, the boiler does nothing.

When the plumber first looked at it he diagnosed a knackered fan, he was right. The fan was stuck, he freed it off, manually spun it and then tried the ignition sequence. It worked.

Came back with a new fan, replaced it, boiler worked fine. My how quiet it was compared to the old fan. Come the next morning the boiler is not working. Same things happening, programmer calls for heat, pump comes on, no boiler.

 

[namsag]

Get him to look at air pressure switch if it sticks in made position after boiler has been on it will stop it going through any of the ignition sequence including fan start up the next time it wants to come on

 

[duffy78]

Thanks namsag,

i'm sure he would have considered this, if i was to check it myself what would i be looking for?

off to google to study pressure switches.

 

[JonB]

I can recommend CombiUK in the B'oro.
JonB

 

[Agile]

and the only reason i brought up the plumber paying for some of the cost of replacing the boiler was because he said he broke the loom whilst replacing the fan, because he says the loom's old and brittle. (the boiler is 15 years old) But forget that now.

The boiler worked after he had changed the fan and didnt work again in the morning, so i thought it might not be the loom as surely the boiler would not have worked after he installed the fan.

I have checked for continuity across the loom and my multi meter says there is no breaks in the wire. but i did not check for a resistance of less than 1 ohm, i just used the buzzer on the meter that says their are no breaks in the wire.

thanks.

In spite of what the plumber said, I doubt that he had broken the loom because as you said the fan would not have worked at all.

Most meters will give an audible tone with up to 30-60 ohms resistance. That can be too high for many boiler circuits and the only sure way is to measure the actual resistance. I have made that mistake some while ago and wasted an hour so never again !

I have no reason to think there is anything wrong with your wiring loom.

There seems a distinct possibility that he said that just to "lock you into" getting him to replace the boiler. Its a good strategy as it has worked!

My suggestion is that you try to find someone who will diagnose the problem on a no-fix no-fee basis. I doubt there is much wrong with it as its a simple boiler.

Tony

 

[Agile]

Thanks namsag,

i'm sure he would have considered this, if i was to check it myself what would i be looking for?

off to google to study pressure switches.

Faced with the prospect of a nice £1700 job of fitting a new boiler it seems very unlikely to me that he has bothered to do that at all. Its not in his interest. If he has any experience of boilers he will know that it is the likely fault.

However, the APS is part of the safety devices and as such should not be touched by a DIYer. Its also a part where measuring with a continuity buzzer will usually give a false impression that its operating correctly.

Tony

 

[duffy78]

i'm checking the thermocouples,

should there be a voltage going to the boiler overheat cut off?

there is one going to the low and one to the high but nothing to the overheat cutoff.

 

[duffy78]

all ive done re the aps is gently blow into it to see if i could hear the microswitch.

 

[Agile]

You should not even be accessing the APS.

If you blow into it you are likely to damage it, You should blow towards it.

You dont test them by listening for a click! That means little, You need to measure the actual resistance of the NO and NC contacts. Needs to be less that one ohm.

I hope that you were not testing your loom with the ends connected to the PCB etc. Any meaningful test should be done with it disconnected to ensure you are not sidetracked.

In any case I think this is all a distraction. Failure to recognise a call for heat is a PCB fault if nothing further happens. If the fan starts up then it is recognising the call for heat.

Tony

 

[namsag]

Agile.
He already told us . The fan doesnt start , nothing happens at all

 

[Agile]

In any case I think this is all a distraction. Failure to recognise a call for heat is a PCB fault if nothing further happens. If the fan starts up then it is recognising the call for heat.

Tony

Reading that again I have noticed that to a DIYer it could be misunderstood.

If there is a fault, for example on the APS, then the PCB may be recognising the call for heat but unable to start the fan because one of the checks it performs has not been satisfied.

In that case the PCB can be recognising the call for heat but not apparently doing anything to someone standing in front of the boiler.

Thats why careful electrical tests on each component in the critical path are essential to identify any faults.

Tony

 

[oph]

Have i misread this but earlier the OP said that there was no voltage on the switch live into the boiler from external demand when there should have been?

If there isnt then its an external fault

 

[onlyfitidealboilers]

sorry dont know this boiler, but is it a three wire or two wire APS?

 

[onlyfitidealboilers]

and the only reason i brought up the plumber paying for some of the cost of replacing the boiler was because he said he broke the loom whilst replacing the fan, because he says the loom's old and brittle. (the boiler is 15 years old) But forget that now.

The boiler worked after he had changed the fan and didnt work again in the morning, so i thought it might not be the loom as surely the boiler would not have worked after he installed the fan.

I have checked for continuity across the loom and my multi meter says there is no breaks in the wire. but i did not check for a resistance of less than 1 ohm, i just used the buzzer on the meter that says their are no breaks in the wire.

thanks.

In spite of what the plumber said, I doubt that he had broken the loom because as you said the fan would not have worked at all.

Most meters will give an audible tone with up to 30-60 ohms resistance. That can be too high for many boiler circuits and the only sure way is to measure the actual resistance. I have made that mistake some while ago and wasted an hour so never again !

I have no reason to think there is anything wrong with your wiring loom.

There seems a distinct possibility that he said that just to "lock you into" getting him to replace the boiler. Its a good strategy as it has worked!

My suggestion is that you try to find someone who will diagnose the problem on a no-fix no-fee basis. I doubt there is much wrong with it as its a simple boiler.

Tony

Tony you seem hell bent on planting a seed in tis boys mind. you are not on the job so you dont know for sure what the problem so dont point the finger at a the poor bloke who has been round there.

not every boiler is worth fixing just because you carnt get your head round soldering!!