Combi boiler, banging pipes and a leak

[Paul]

We have a gas combi boiler.

A few weeks ago the pipes started banging when filling the bath with hot water. Around the same time we noticed a (very slow) leak under the boiler. I've been tightening the connection that leaks a little at a time (30 or 60 degrees at a time). The leak has slowed but not stopped. The banging seems to have stopped.

Could the two be connected? Indeed, could one be causing the other?

If I can't stop the leak, can I just turn the water off at the stop cock, drain the system and replace the connection, or is this definitely one for the pros?

[Blodwyn Pig]

OK, the banging, when you run the bath.  When this happens next,  have a look at the digital temp gauge on the boiler,  it'll prob be much higher than it should be, prob around 90-95 deg. Also the boiler will prob be banging as well.  I think the problem is you heat exchanger is clogged up with gunk. The water passageways are tiny, so as to be most effective. Now when you call out a plumber, he will probably tell you that you need a new one, as you can't clean them.  This is 100% wrong, you can clean them very effectively.  When the heat exchanger is removed,  then fill a bucket with  clean water,  and add some 'spirit of salts' into the 4 holes of the HE, filling it up,  then place the HE in the bucket of water, and wait for the action. Much fizzing, popping, and general merriment, for 10 mins, then swish it around, then rinse with clean water.  The old water will be black, and full of bits.  Had mine done twice now, costs about £45 at go, ( at least 2 years apart)  to take out clean and re fit, but that's prob cheap.

[Paul]

OK, the banging, when you run the bath.  When this happens next,  have a look at the digital temp gauge on the boiler,  it'll prob be much higher than it should be, prob around 90-95 deg. Also the boiler will prob be banging as well. 

Yes - the boiler does bang too. I'll do the temp check.

I think the problem is you heat exchanger is clogged up with gunk. The water passageways are tiny, so as to be most effective. Now when you call out a plumber, he will probably tell you that you need a new one, as you can't clean them.  This is 100% wrong, you can clean them very effectively.  When the heat exchanger is removed,  then fill a bucket with  clean water,  and add some 'spirit of salts' into the 4 holes of the HE, filling it up,  then place the HE in the bucket of water, and wait for the action. Much fizzing, popping, and general merriment, for 10 mins, then swish it around, then rinse with clean water.  The old water will be black, and full of bits.  Had mine done twice now, costs about £45 at go,  to take out clean and re fit, but that's prob cheap.

Noted.

[Blodwyn Pig]

oh, and forgot to say, the 'leak' may not be where you think it is.   Could be an 'o' ring somewhere, quite likely, or,  at the very top of the boiler,  somewhere,  there will be a pressure relief valve, a small gold coloured cylinder, prob 3" dia, and 3" high, with a small valve on the side, this could be letting excess pressure (and a wee drop or two) out, when the boiler is banging. Run your fingers around this to check for wet. I wouldn't keep tightening things up willynilly. If poss, take off the front cover,and gently feel for water on wires, pipes etc , and try to trace the source.  It is prob coming from the valve on top, and dribbling down inside, behind the casing somewhere.  Best of luck.

[neilrj]

Nipping a joint up works fairly often but only for under-tightened joints, it is very easy to overtighten and distort any joint to the point it gets much worse, and then frankly they can almost gush (DAMHIKT, it was 30 years ago). CH leak sealers can be purchased from Screwfix/Toolstation/or even a real plumbers merchants, and these will often see off a small leak, even on pressurised systems, and for our older readers these sealers are the equivalent of an egg in a car radiator   and I know raw egg or Radweld (TM) rather dates me.
My money is on Blodwyn's diagnosis of clagged heat exchanger (and leak is coincidental) and descaling is just the same as doing a kettle/coffee machine but at Gas Safe rates.

[Kim]

Run your fingers around this to check for wet.

I've found that tying a strip of kitchen roll around the pipe can be a good way to detect leaks, especially when there's condensation.


Are we sure it isn't just water hammer from a dodgy bath tap?

[Blodwyn Pig]

Run your fingers around this to check for wet.

I've found that tying a strip of kitchen roll around the pipe can be a good way to detect leaks, especially when there's condensation.


Are we sure it isn't just water hammer from a dodgy bath tap?

Good point about the tissue, yes I often use a strip of loo roll , tied around below a joint, as condensation is also wet.

Could be the tap, hence checking the water temp on screen, it will fluctuate as well. Should also do it on kit sink tap also, it's just that bath tap runs for much longer, so boiler gets hotter.

[Aunt Maud]

As Kim rightly said, check tap and bog roll the joint before playing with the boiler. It is christmas time after all, so you may have fun getting any sensible plumber types to turn up.

[Gattopardo]

OK, the banging, when you run the bath.  When this happens next,  have a look at the digital temp gauge on the boiler,  it'll prob be much higher than it should be, prob around 90-95 deg. Also the boiler will prob be banging as well.  I think the problem is you heat exchanger is clogged up with gunk. The water passageways are tiny, so as to be most effective. Now when you call out a plumber, he will probably tell you that you need a new one, as you can't clean them.  This is 100% wrong, you can clean them very effectively.  When the heat exchanger is removed,  then fill a bucket with  clean water,  and add some 'spirit of salts' into the 4 holes of the HE, filling it up,  then place the HE in the bucket of water, and wait for the action. Much fizzing, popping, and general merriment, for 10 mins, then swish it around, then rinse with clean water.  The old water will be black, and full of bits.  Had mine done twice now, costs about £45 at go, ( at least 2 years apart)  to take out clean and re fit, but that's prob cheap.

Is spirit of salts ok for aluminium?
 

[Blodwyn Pig]

OK, the banging, when you run the bath.  When this happens next,  have a look at the digital temp gauge on the boiler,  it'll prob be much higher than it should be, prob around 90-95 deg. Also the boiler will prob be banging as well.  I think the problem is you heat exchanger is clogged up with gunk. The water passageways are tiny, so as to be most effective. Now when you call out a plumber, he will probably tell you that you need a new one, as you can't clean them.  This is 100% wrong, you can clean them very effectively.  When the heat exchanger is removed,  then fill a bucket with  clean water,  and add some 'spirit of salts' into the 4 holes of the HE, filling it up,  then place the HE in the bucket of water, and wait for the action. Much fizzing, popping, and general merriment, for 10 mins, then swish it around, then rinse with clean water.  The old water will be black, and full of bits.  Had mine done twice now, costs about £45 at go, ( at least 2 years apart)  to take out clean and re fit, but that's prob cheap.

Is spirit of salts ok for aluminium?

Don't know, thats what my plumber uses, maybe HEs are Stainless.   

[Mrs Pingu]

Personally, I would be more inclined to use acetic acid (vinegar). Spirit of salts appears to be HCl which is a 'strong' acid and a bit aggressive to metals. If it's mainly carbonate scale in the h/ex acetic will be fine. If it it's a mixture of carbonate scale and metal oxides & stuff you might dissolve enough carbonate to allow you flush all the other crap out.

P.S. IANA CH boiler engineer but dissolving scale is part of my day job....

[Jurek]

Personally, I would be more inclined to use acetic acid (vinegar). Spirit of salts appears to be HCl which is a 'strong' acid and a bit aggressive to metals. If it's mainly carbonate scale in the h/ex acetic will be fine. If it it's a mixture of carbonate scale and metal oxides & stuff you might dissolve enough carbonate to allow you flush all the other crap out.

P.S. IANA CH boiler engineer but dissolving scale is part of my day job....

My bold.
Word.
One gets to meet the best people on here.

[Gattopardo]

Is spirit of salts ok for aluminium?

Don't know, thats what my plumber uses, maybe HEs are Stainless.   

Can be either, as Mrs Pingu said HCL seems a bit harsh.  If it is scale I'd fit a descaler on to the inlet, as you are currently supposed to have, I use citric acid and have in the past and agitaed the exchangers.

[Paul]

Are we sure it isn't just water hammer from a dodgy bath tap?

What a good call. I knew the washers needed looking at anyway so replaced them. Pipe banging gone. Thanks Kim and all.

The leak persists but very slowly. Will call an expert after the festivities.