Main heat exchanger small leak

[trevorbayliss]

I have a valiant 837 eco combi. It is 18 yo this April.

It has been loosing pressure now for a year approx.

I have no leaks on my system and so the engineer thinks it is the heat ex. He recommended using some leak sealer and I think that slowed the leak down.

It is loosing pressure over a two week period and goes down from 1.4 bar to 0.9 in this time. I notice the pressure is now dropping a little faster so maybe the leak sealer has only done so much. I added it in aug 2025.

My question is about the length of time we can keep this boiler going. Everything else is working well, the system is very clean as I have a magna clean pro2 on it (just cleaned the filter this morning). How do these issues deterioate over time? Will the HE really break at some point and so make the system not function. Ideally I will change the boiler over in the summer, my engineer knows about it and he can do it quite quickly if I need him to.

 

[Fred Blogs]

How long is a piece of string basically. If you are going to change the boiler in the summer anyway and you are happy to top it up every so often then leave it. You say your boiler man can change it quite quickly so leave it. If it breaks down completely then get your man to change it if it goes until you decide to change it in the summer all well and good.

 

[Harry Bloomfield]

I have no leaks on my system and so the engineer thinks it is the heat ex.

Thinks? The usual test, when the boiler includes a pressure gauge, and the means to isolate the boiler - is to pressurise the system, isolate the boiler, then keep an eye on the gauge. If it drops, the HE has leak, if not it doesn't.

 

[trevorbayliss]

Well it has been ongoing for ages and in the summer when the heating is not on the pressure doesn't drop. We have no visible area of damp in the ceilings. The area we cannot tell is the UFH circuit in the kitchen. This is plastic pipe in concrete. Can this pipe leak ? It is about 18 yrs old as well.

 

[denso13]

It's 18 years old, run it till it breaks, then get your guy to change it.

 

[CountryFan]

The area we cannot tell is the UFH circuit in the kitchen. This is plastic pipe in concrete. Can this pipe leak ? It is about 18 yrs old as well.

I'm no ufh expert, but I'd say yes. Over the period you say it drops I can't see it being the main heat exchanger.

 

[Harry Bloomfield]

Can this pipe leak ? It is about 18 yrs old as well.

Same method, as testing the HE - fit a pressure gauge, and a means to isolate at input and output. Pressurise, isolate, and keep an eye on the gauge.

 

[trevorbayliss]

I suppose I do need to find out whether the UFH is leaking before I switch to a new boiler.

 

[CountryFan]

I suppose I do need to find out whether the UFH is leaking before I switch to a new boiler.

Yep, or get the same thing.

Personally, I would Isolate the boiler from cold first thing into the morning, leave it all day and open the valves back up. If the pressure has dropped before you open the valves the issue is at the boiler, if it drops after opening the valves then it's on the system

 

[denso13]

I'

I suppose I do need to find out whether the UFH is leaking before I switch to a new boiler.

I'd be very wary of touching the boiler isolation valves on an old boiler.

 

[trevorbayliss]

This is my UFH manifold. One of the flow indicators is very black.

 

[CountryFan]

This is my UFH manifold. One of the flow indicators is very black.

Not sure on that, but looks like it's shouldn't be black. Also the bleed vent looks like it's leaked previously.