Mini C28 boiler cuts out after short use of hot water

[Slaine1674]

Hello,

I had success here in the past in fixing my boiler so need help again:

//www.diynot.com/forums/viewtopic.php?t=157694

My mini C28 combi boiler recently has another problem in which the ignition cuts out and the boiler gets stuck in a loop trying to ignite.

It seems to happen much quicker during hot water use rather than central heating, although i have noticed the problem occurs with the heating eventually too.

Hot Water operation after around 2-15 mins
Heating after around 30 minutes

If I switch the system off for a while it repeats the process after "cooling" down.

There is enough gas and water pressure is at 1.5 cold and 2 heated.

I can hear the pump start and the clicking of microswitch, I have not checked to see if fan is spinning but I imagine it is as heating has been running for 25 mins as I write this on a heating test.

But as soon as a I try hot water running it jumps to the problem.

The diagnostic lights show the fault for "lack of burner ignition" once the boiler works out it has a fault when it goes into the ignition loop with no spark. It is a whiring sound start and stop, start stop etc

Is this a fault with pcb 2 board on the right?

I have photos below of the front and back which looks like some heat damage to the resistors, so when they heat up they are breaking the circuit and causing the sequence on the board to fail.

Untitled

• Slaine1674
• 18 Jun 2012
• 1

Untitled

• Slaine1674
• 18 Jun 2012
• 1

Untitled

• Slaine1674
• 18 Jun 2012
• 1

Untitled

• Slaine1674
• 18 Jun 2012
• 1

My model number is posted as below:

Untitled

• Slaine1674
• 18 Jun 2012
• 1

I hope that you can help.

Many thanks in advance

 

[Agile]

Hello,

I have photos below of the front and back which looks like some heat damage to the resistors, so when they heat up they are breaking the circuit and causing the sequence on the board to fail.

I hope that you can help.

Many thanks in advance

So why do you think the resistors are breaking the circuit?

 

[Slaine1674]

I may be totally wrong and irrelevant, but was just trying to be logical, had a similar problem on a tv circuit board once, the tv repair guy, showed me back of board which when the resistor connection got hot the connection got broken, applied new solder to bridge it and it worked, cheap fix and tv worked for years after.

Read over 80 posts on the mini c28 before submitting the post, so I was trying to narrow down the problem to get an informed response from the experts, rather than waste their time asking me to repeat the same answers they have given before.

You helped me last time and I sent you the faulty part to use for training as requested. Do you have any more thoughts on my problem?

Regards.

 

[Agile]

I very much doubt that resistor is causing the problem.

But you could reflow the solder to be sure. Look at other joints closely and see if you can see any cracking of the joint particularly on the relays.

A way to see if a joint is going faulty is to measure the voltage across ir or easier to chassis from each end. But usually a faulty joint is visible.

If none of that helps you could monitor the voltage sent to the fan at the PCB ! Dont open the combustion chamber though as we dont advise DIYers to do that.

Can you describe the symptoms any better?

Tony

 

[Slaine1674]

Hi Tony,

thanks for your quick reponse. I guess one thing is that the problem seems intermittant at the moment. I'm having trouble narrowing down any consistancies.

This morning and last night the hot water ran faultlessly for over 20 minutes and the heating for over 40 minutes. But the problem has occurred a number of times over the last week with no real pattern and sometimes it happens after running the hot water for 2 minutes and sometimes not at all even after 20 mins.

As I write reply, this the hot water is running for 10 mins and temperature is around 58 degrees pressure at 2 bar running as normal no unusual sounds or noises.

I just want to resolve it now in case it can lead to further problems. Is this a warning sign of more problems to come?

I will check the board again but couldnt see any obvious breaks in connection. Testing the voltage will take me a bit longer to do as need the help of my dad for that!

Regards

Russell

 

[Agile]

Dont go looking for faults that are not occuring.

Look closely at each solder joint with a mag glass!

Remake any bad ones.

Might be a relay contact, particularly the fan relay.

Tony

 

[Slaine1674]

Somthing occured to me whislt reading the forums again. I said earlier that when using diagnostic mode that the led code indicated a lack of burner ignition. But that is only after a few moments of trying to start up again once the boiler had cut out.

I'm at work now, but seem to recall then when hot water is ran from the tap, that the red led is not on for led 2. Is this led meant to light red in normal normal operation for hot water?

In which case does this indicate faulty primary flow switch? Does this tie in with my other symptoms?

Will test when I get home.

Many thanks again.

 

[Slaine1674]

Just ran hot water at home and hot water runnning with led 2 not red, just one flashing green on left 1 sec on 1 sec off alternating with led 3. Is this normal?

I have the boiler servicing/installation user guide and so was just following the troubleshoot trees but getting confused on matching symptoms.

I don't intend to self-diagnose but I guess I am acting too keen to solve issue!

Apologies and await any further expertise and guidance for next steps if it is not an electrical issue.

 

[Agile]

The two green alternating is the normal demand for DHW when in the diagnostic mode which is probably what I showed you how to do before.

The central red light is always part of a fault condition.

Tony

 

[Slaine1674]

Ok. Will look at the board connections then next.

Many thanks.

 

[Slaine1674]

I couldn't see any problems with pcb 2 on closer inspection but have touched up the connections near the discolored area.

I will try pcb 1 too, if this does not solve the issue.

One thing I have noticed is that the flame through the inspection window, I feel is burning with a more orange coloured flame, than I remember.

I recall it burning always blue, with not really any tinge of orange. Now it is probably 50% orange coloured.

Is this related to my problem?

Are there impurities or flow issues causing the "mix" to be wrong and so the system is shutting off?

Many thanks.

 

[Agile]

Probably no problem but since that is gas related we dont advise here.

On that model the flames near the viewing window are impinging on the ignition and detect electrodes which impart a yellowish tinge anyway.

I know its difficult to get people to understand this but the discoloured PCB substrate is NORMAL and not an indication of a fault location. More likely to be on the fan relay connections!

Not likely to be a joint on the control PCB.

Tony

 

[SortedPlumbing]

I couldn't see any problems with pcb 2 on closer inspection but have touched up the connections near the discolored area.

I will try pcb 1 too, if this does not solve the issue.

One thing I have noticed is that the flame through the inspection window, I feel is burning with a more orange coloured flame, than I remember.

I recall it burning always blue, with not really any tinge of orange. Now it is probably 50% orange coloured.

Is this related to my problem?

Are there impurities or flow issues causing the "mix" to be wrong and so the system is shutting off




Time for a gas engineer

Many thanks.

 

[Slaine1674]

Just to conclude. Now Fixed!

Problem solved from resoldering several dry joints on back of pcb 2. Simple fix took less than 10 mins.

(Flame colour issue was my imagination - no problem there!)

These forums are excellent, my ability to search through the long post history on diynot.com of relevant problems shared and solved, meant I could zero in on a problem and help get an answer, again.

All thanks to the prossionals who give their time freely here.

Especially Username Agile, who has helped for the second time in 4 years.

Thank you to all your help once again Tony.

Regards,


Russell