How to seal a leaking U bend joint?

[GNNMartin]

My heating system empties condensate via a U bend. The boiler generates ferric oxide. That is a worry in itself, but the boiler is nearly 20 years old and I can see no sign that the heat exchanger is being significantly eroded, so that is not what concerns me here. Part of the boiler's service routine recommends checking the U bend is not getting clogged (by ferric oxide?). I did this recently, but after re-assembling the U bend, one junction leaks.


I've taken it apart again, and I can't see why it should, and I'm wondering what to try next. I know from unhappy experience that if I buy a U bend from my local plumbers' merchant there is a good chance that it will not be a swap-in fit, and access is difficult so I want to avoid anything leading to major modification. I thought of using some Fernox LSX on the joint, but that will make it even harder to re-assemble next time I take it apart to check it is not clogged.


I wonder if there is some less aggressive sealer that anyone can recommend. Perhaps just silicon grease, since there will be no pressure? Any ideas?
Nigel Martin

 

[stevetheplumber]

probably a job for some ptfe tape have you check the washer is in place properly ? which boiler have you got sounds funny that its 20 years old and producing condensate of is it open flued with a condense drain on the flue

 

[chris watkins]

Nigel, I bet you wish you had employed a Gas Safe Registered engineer to carry out your boiler servicing as this would be their problem now. They would also have carried out flue gas testing to ensure correct combustion & operation of the boiler.
Sorry if you feel this is a negative answer. BTW burning gas does not produce ferric oxide, it is nitric acid, as far as I am aware.

 

[GNNMartin]

Steve, thanks. I do plan to try PTFE tape when I can work up the energy to wriggle into the narrow space again. I don't have great hopes given the design of the joint. I did check the washer was in place, and that it looks OK. The boiler is a very early condensing boiler (Keston).
Nigel

 

[GNNMartin]

To my very pleasant surprise, the PTFE tape seems to have done the trick. Thank you. I didn't think there was enough space to wrap the tape, and thought it would just displace when tightening up. But, touch wood, its been in place for an hour now with the U bend topped up, and there has been no leak detected so far.
Nigel

 

[GNNMartin]

Nigel, I bet you wish you had employed a Gas Safe Registered engineer to carry out your boiler servicing as this would be their problem now. ... . BTW burning gas does not produce ferric oxide, it is nitric acid, as far as I am aware.

Chris, thanks for the (albeit negative) post. My experience of Corgi plumbers has been that it is generally better to do the work myself. It is not much consolation to know it is someone else's fault if that means waiting for them to come back and fix the problem. I do have an engineering background.

The stuff that I have called ferric oxide consists of back granules that form on the heat exchanger. I assume they are ferric oxide because they look like ferric oxide, and I can't think what else they could be. Ferric oxide is basically rust, though in its most oxidised form, and while I assumed that the heat exchanger was made of stainless steel it is not by any means unbelievable that it should corrode to form ferric oxide particles. Actually, the heat exchanger does not look 'bright', so perhaps I was wrong in thinking that I remembered it to be stainless steel.

Anyhow, thanks to Steve I seem to have fixed the problem. I was thinking of having a go with PTFE tape, but it is such a pig to get at the U bend, and I had so little confidence that PTFE could fix the problem, that I posted here before trying it.
Nigel

 

[Dotty]

Chris, thanks for the (albeit negative) post. My experience of Corgi plumbers has been that it is generally better to do the work myself. It is not much consolation to know it is someone else's fault if that means waiting for them to come back and fix the problem. I do have an engineering background.

The stuff that I have called ferric oxide consists of back granules that form on the heat exchanger. I assume they are ferric oxide because they look like ferric oxide, and I can't think what else they could be. Ferric oxide is basically rust, though in its most oxidised form, and while I assumed that the heat exchanger was made of stainless steel it is not by any means unbelievable that it should corrode to form ferric oxide particles. Actually, the heat exchanger does not look 'bright', so perhaps I was wrong in thinking that I remembered it to be stainless steel.

Anyhow, thanks to Steve I seem to have fixed the problem. I was thinking of having a go with PTFE tape, but it is such a pig to get at the U bend, and I had so little confidence that PTFE could fix the problem, that I posted here before trying it.
Nigel

Engineering background or not it is illegal to work on gas fired appliances without being able to prove your competence. And this competence comes in the formal training, rigorous testing and ongoing inspections.

How much consolation will you have if you've missed or ignored a safety critical part of the boiler and are currently poisoning your family!

GET A GSR IN NOW!

 

[chris watkins]

That the trouble Nigel a plumber would have PTFE'd the treads in the first place so there would not have been a leak on the TRAP (in plumbing we do not call them U bends) to come back to.
You typify the old saying that a "little knowledge is a dangerous thing". Don't forget that when your Keston ferric oxides it's self away there is no need to call-in a "Corgi plumber" to comply with the Law, you just buy a new one & fix it up yourself.

 

[CMcM]

Engineering background or not it is illegal to work on gas fired appliances without being able to prove your competence. And this competence comes in the formal training, rigorous testing and ongoing inspections.

How much consolation will you have if you've missed or ignored a safety critical part of the boiler and are currently poisoning your family!

GET A GSR IN NOW!

Yet we still help joe blogs with answering how to solve these wee issues. now he has a bit more confidence and will prob attempt something else again and again untill we see it in the news that his latest DIY didnt go so well..... Then we have to pay to do more tests to make sure we dont do what he done haha

 

[Dotty]

Yet we still help joe blogs with answering how to solve these wee issues. now he has a bit more confidence and will prob attempt something else again and again untill we see it in the news that his latest DIY didnt go so well..... Then we have to pay to do more tests to make sure we dont do what he done haha

I agree. But unfortunately the op didn't reveal until post 6 that he'd been servicing his boiler himself. Had he shared that little nugget of information sooner he'd have had a completely different response. I doubt the engineering background tbh. He would've had a better understanding of the sealing and non reactive properties of ptfe if he had what he said. As Chris said, a little knowledge isa dangerous thing!

 

[REDSAW]

my uncle was an 'engineer' he used to make bolts for weapons on his lathe.

he could take any machine with nuts and bolts to bits.

they used to call him 'humpty dumpty'

 

[Billy Bob Bob]

we have someone come on here who is servicing there own boiler,yet has to ask for advice on how to fix a simple leak frightening really,as said a little knowledge is a dangerous thing, for that reason i am closeing this thread