Undersized boiler do not use

[Peterb147]

Hi I've been to a customer today that has a 9 year old baxi duo tec40kw boiler,it runs 20 radiator that all work fine,they have 2 bathrooms and 1 electric shower and again have no issues with hot water.Over the last 4 years baxi have repaired the boiler on 8 occasions, with faults on gas valve expansion tank main heat exchanger and sensor faults.They have had baxi out today as there was a leak on the boiler and the engineer has put a do not use label on the boiler and said that the boiler is undersized and should not be used.Has any one got any advise on this as I thought you would only label a boiler with a do not use if there was a safety issue with the boiler.TIA

 

[ShaunCorbs]

Needs to be unsafe for them to label so need more information

 

[Peterb147]

Needs to be unsafe for them to label so need more information

That's what I've told the customer and there is no other issue with the boiler as i fitted it 9 years ago.He said the baxi engineer just said it was too small for the house and put a do not use label ,it hasn't been turned off or a warning notice issued Baxi have fixed this numerous times and never said anything on all previous visits

 

[ShaunCorbs]

Needs to be a reason best bet is for you to phone baxi up and ask them why there’s a danger do not use and no paperwork left on site

 

[Last Plumber]

Is it undersized?
If it is running at full knacker constantly, that can lead to the trap drying out which presents a potential issue safety wise.

 

[John-sjw]

Is it undersized?
If it is running at full knacker constantly, that can lead to the trap drying out which presents a potential issue safety wise.

It will still be producing condensate, so that does not hold.
The boiler may be undersized when -3 outside, otherwise it is fine. Do a heat loss calculation.

 

[Last Plumber]

It will still be producing condensate, so that does not hold.
The boiler may be undersized when -3 outside, otherwise it is fine. Do a heat loss calculation.

I have seen over-sized and undersized boilers with dry traps.
It does depend how over-sized or undersized they are amongst other things but it is possible for a trap to dry out and leave a situation where the products of combustion are flowing through the condensate pipework. Wouldn't you agree?

I am not saying that this is the case here but as no-one knows why the user was told that it should not be used and that it had been labelled by baxi, I thought it was a good place to start. My thinking was a reason of safety but obviously I wasn't there.

Maybe he just ran out of 'undersized boiler' stickers!
Who knows.

 

[John-sjw]

I have seen over-sized and undersized boilers with dry traps.
It does depend how over-sized or undersized they are amongst other things but it is possible for a trap to dry out and leave a situation where the products of combustion are flowing through the condensate pipework. Wouldn't you agree?

I am not saying that this is the case here but as no-one knows why the user was told that it should not be used and that it had been labelled by baxi, I thought it was a good place to start. My thinking was a reason of safety but obviously I wasn't there.

Maybe he just ran out of 'undersized boiler' stickers!
Who knows.

I have only seen condensate traps dry out after extended idle use. Safety? All can happen is exhaust gasses blown down through the trap into the drain or outside. OK this may mean gasses into a kitchen via the waste trap connection usually used for washing machines, all depending on how it is piped up.

It needs a heat loss calculation for sure. Firstly the size of the boiler for the premises has to be determined. Even then, if it is slightly undersized for the worse case example (-3C outside) I cannot see the trap not filling with condensate.

 

[Last Plumber]

I have only seen condensate traps dry out after extended idle use. Safety? All can happen is exhaust gasses blown down through the trap into the drain or outside. OK this may mean gasses into a kitchen via the waste trap connection usually used for washing machines, all depending on how it is piped up.

It needs a heat loss calculation for sure. Firstly the size of the boiler for the premises has to be determined. Even then, if it is slightly undersized for the worse case example (-3C outside) I cannot see the trap not filling with condensate.

I am only telling you what I have seen.
I wouldn't leave a customers boiler on knowing that the trap is capable of drying out, as the condensate drain is not designed to carry flue gases. Yes it does depend how it is piped. It may not be air tight.
The reason the Baxi chap left a safety note is unknown so it might be nothing to do with dry traps. I was thinking out loud over why it would be labelled that way for being undersized. I can't think of a reason other than that. There might be one I haven't thought of. I have never told a customer that an undersized boiler is unsafe.