Is my brain working....

[secret squirrel]

On Tuesday I've got to go and have a look at a vailant 620 system boiler that has an intermittent fault.

I am going with a friend of mine whose gas safe etc but has given me the details of what he's found and wants to test my brain. I have explained that he's barking up the wrong tree with than but I'll try anyway.

The fault is the boiler shuts down randomly for no apparent reason but as soon as it resets it comes back into life. It is running an average size house.

Boiler is in the loft with the unvented h/w cylinder and 2 x 2 port valves which are approx 1m away from the boiler.

The programmer comes on at the same time for both h/w and heating. There is no external auto bypass valve. There was a dodgy TRV and air in one of the rads.

The occupant of the house has been in there for approx 2 months and this is the first system boiler they've owned.

My theory is the TRV and air are unrelated to the boiler issue.

With regards to the boiler:

the 2 x 2 port valves are very close to the boiler and if the h/w and heating are satisfied at the same time, both valves close, then the boiler can't get rid of the heat quick enough so locks out. By the time the house holder realises and re-sets the boiler everything has cooled down so the problem has gone, until the next time.

I think its intermittent because both valves may not shut down at the same time.

OK, the flaw with my theory is if the boiler is fitted with an auto bypass, faulty? probably not. I still think if the boiler has an auto by pass the hot water can only go a distance of 1m?

Am I along the right lines?

 

[southcoastboile]

would have thought the boiler would cut out on its stat before it overheats, when the valves close it cuts the power to the boiler so the boiler shouldn't carry on running, could be a circulation fault if its overheating, check the pump and turn the boiler stat down and see if this helps, also could be something to do with air in the system, just make sure all the rads and air vents are bled, wouldn't think it has anything to do with a bypass

 

[CES]

There is an auto bypass fitted to this boiler, have you checked the fault codes to see what is shutting it down?

 

[secret squirrel]

There is an auto bypass fitted to this boiler, have you checked the fault codes to see what is shutting it down?

I've been told that it is so intermittent and the customer has no knowledge of fault codes, I've asked my friend whose looking at it on Tues where do you even start with an intermittent fault.

He was very illusive about it and said 'you have a think and I'll see you on Tuesday'

Unfortunately, curisoty has definetly got the better of me here.

 

[CES]

There is a fault history within the control on the boiler. Its stores the last 10 faults. press "i" and "-" together then use "+" to scroll through. Theres a list within the MI's that have proven to be useful in the past.

 

[secret squirrel]

Thanks for the replies,

My gas expert who looked at the boiler today was impressed with my knowledge and agreed totally about the bypass valve.

He questioned the householder at length, tested loads of things, looked up the fault codes but nothing was clear, tested thermistors with multi metre, flow and return temps etc.

The advice was when/if it happens try and get hold of me or my friend, we will come round and have a look with the fault which has caused the stoppage.

I explained that I'm not gas safe (as he already knew) but he said I'm more than capable to run a couple of tests with him at the end of the phone. Customer happy (not charged) and I was chuffed as well.

 

[markfxy]

Had the same thing at the weekend boiler fired up and ran for 5 minutes then locked out turns out the stopcock to the f&e tank was shut off tank empty and pump running dry!