System dropping pressure every few days

[morepunk]

Posting this on behalf of my Nan who has been experiencing issues with her central heating system periodically for the a number of years, and thus far no-one has offered a solution that has provided a permanent fix.

She lives in a 1970s bungalow with central heating throughout. The combo boiler is around 15 years old and is in her kitchen, she has an immersion heater in a tank in the airing cupboard.

At the moment, every few days she’s losing enough pressure in her system meaning that she has no hot water. She has to call out my Dad to repressurise the system every time it happens. She can use the immersion heater as a backup, but it’s not ideal, and we’re thinking ahead to the winter when the issue will affect her heating.

The fixes that have been applied previously are:

• A replacement of the immersion heater (this happened without the rest of the family’s knowledge, and the immersion heater never actually had an issue as far as we know)
• Leak sealant applied to the system.
• Some other repair that was described to me as something that inflates inside the system - I have no idea what it is though.

She has the boiler serviced annually and has insurance to cover the boiler and the system, but not pipework.

Recently she’s had an engineer out on 2 or 3 occasions, but anything they’ve attempted hasn’t resolved the issue. The latest engineer’s notes were that there’s a leak in the system, but he can’t identify from where. He told my nan that her boiler is fine despite its age, and that it isn’t the cause of the issue.

Most of the pipework in the house is exposed, and neither my Nan or Dad can see a leak anywhere. With it being such a small house, they expect that if there was a leak in the pipework that causes the pressure to drop by 1 bar every few days, that there would be some sign of the leak.

Because this has been going on for so long, and there have been multiple engineers that have looked at it without providing a permanent fix, my Nan doesn’t know what to do next. She’s willing to get the boiler replaced if need be, or to get whatever pipework replaced if there is a leak, but no-one seems to be able to help in confirming what/where the issue is.

If anyone can offer any advice, perhaps with how we can try to diagnose the issue, or whether there’s something obvious that could cause this issue, it’d be a great help and hugely appreciated. I understand that the best way to diagnose an issue is to see it physically, but because my Nan hasn’t had any luck with that route she’s lost faith in local engineers.

 

[Thommo]

If you’ve had numerous engineers come out onsite to inspect both the immersion heater and the Combi then the fault likely does lie within the pipework, given the pressure drop amount it could be indicative of a small leak on the system or multiple small leaks.

Dependant on availability in your area it may be a better and cheaper option to have a leak detection specialist come out to inspect the pipework.

They will conduct acoustic location tests, tracing gas tests, thermal imaging etc etc.

 

[oz-plumber]

Replace expansion tank and PRV.

If you can't see any leaks, this would be the cheapest solution.
If the pressure drop persists, then go look further.
But for a 15 year old boiler, this is what I would do

 

[Stigster]

The very first thing to do is find the expansion relief pipe (colloquially known as the "blow off" pipe") and go and see if it is actively dripping. If it is dry there, cut the finger off a cheap rubber glove or use a little sandwich bag or similar and tie it over the end of the expansion relief pipe with a rubber band or piece of string. This will either blow right off if it discharges quickly or collect water if it's a slow leak. You must not put any kind of fitting on that pipe, just something like I describe.

Check it after a top-up in a day or two and see if you can find water coming from that pipe. If so there's two likely causes, generally speaking. It'll probably be the expansion vessel is kaput or simply needs recharging (that's the "something" that inflates inside the system). If the expansion vessel proves to be in good order, it'll almost certainly be the pressure relief valve letting by and that'll need replacing.

There are a couple of other potential causes like system overheating and therefore going over pressure or a connected filling loop letting by but do the test on the expansion relief pipe first as it's easy to do and will help to eliminate that side of things as the cause.

 

[morepunk]

Replace expansion tank and PRV.

If you can't see any leaks, this would be the cheapest solution.
If the pressure drop persists, then go look further.
But for a 15 year old boiler, this is what I would do

The very first thing to do is find the expansion relief pipe (colloquially known as the "blow off" pipe") and go and see if it is actively dripping. If it is dry there, cut the finger off a cheap rubber glove or use a little sandwich bag or similar and tie it over the end of the expansion relief pipe with a rubber band or piece of string. This will either blow right off if it discharges quickly or collect water if it's a slow leak. You must not put any kind of fitting on that pipe, just something like I describe.

Check it after a top-up in a day or two and see if you can find water coming from that pipe. If so there's two likely causes, generally speaking. It'll probably be the expansion vessel is kaput or simply needs recharging (that's the "something" that inflates inside the system). If the expansion vessel proves to be in good order, it'll almost certainly be the pressure relief valve letting by and that'll need replacing.

There are a couple of other potential causes like system overheating and therefore going over pressure or a connected filling loop letting by but do the test on the expansion relief pipe first as it's easy to do and will help to eliminate that side of things as the cause.

This is really helpful advice from both of you - huge thanks. We'll start with the glove test and will move to replacement of the expansion tank and PRV as needed. Thanks again!

 

[Aquarius]

You could try and isolate the flow and return under the boiler, and not use the boiler for anything (use the immersion for hot water). Set the pressure to a number (if there is one) or make a pencil mark on the gauge. Leave this overnight and return, if the pressure has dropped it’s at the boiler, if it hasn’t it could be on the heating side. If however you open the valves up and the pressure drops, then it’s definitely on the heating side.

 

[Scott_D]

Are you sure it’s a combi boiler and hot water cylinder?
What make and model boiler?