New combi boiler fitted, system losing pressure. What to do?

JCDUB · 21-01-2021 8:54am #1

I recently had a Baxi combi boiler fitted in a 2 bed mid terraced house.

Immediately after it was fitted it started losing pressure, and had to be re-pressurised using the little valve at the bottom of the boiler. This was happening maybe once every couple of days.

I told the plumber and he came back and said there's probably a small leak in the system somewhere, and that he didn't see anything anywhere when he was fitting.

He said the leak could have been there historically (it's an old house and system) and basically, that's it's not part of his job of fitting the boiler to go looking for a leak in the system. He told me to have a look myself, which I did and saw nothing, although obviously plenty of pipes aren't visible etc.

He put a bottle of that Tec 7 plumbing "sealer" stuff into the system and it was fine for a few weeks.

However it's back to losing pressure and having to be manually topped up every day, which is ridiculous. There's also potentially a leak within my house, which is not good.

What are my options? Is this something he should remedy as the boiler fitter? I would have thought yes, as this wasn't an issue with the old boiler. It's only started happening with the new boiler.

Any advice appreciated. Thanks.

Sleeper12 · 21-01-2021 9:41am

JCDUB wrote:

However it's back to losing pressure and having to be manually topped up every day, which is ridiculous. There's also potentially a leak within my house, which is not good.

What's more important here is you are putting fresh water into the system every day. Fresh water will corrode your system from the inside out eventually. It could void the boiler warranty too.

Plenty of great heating plumbers on here can advise better than me. There are leak detection companies out there. They aren't cheap

John.G · 21-01-2021 10:30am

Just a few easy things you can check yourself, when you re pressurise, see what the pressure rises to when system hot.

Try and see where the condensate pipe from the boiler goes and see if water is dripping from it with the boiler off, you may have to disconnect it somewhere to see this.

JCDUB · 21-01-2021 1:03pm

John.G wrote: »

Just a few easy things you can check yourself, when you re pressurise, see what the pressure rises to when system hot.

Try and see where the condensate pipe from the boiler goes and see if water is dripping from it with the boiler off, you may have to disconnect it somewhere to see this.

Pressure rises to 1.5bar when I re pressurise it. Think it stays there when hot although I'll have to check. I'll also check the condensate pipe and see if it's wet.

Thanks for info.

youtheman · 21-01-2021 2:27pm

Was the old system pressurised? If it was you'd like to think that the operating pressures haven't changed, so the old pipework hasn't been subject to a higher pressure than before so unlikely to be the source of the leak. It the old system was unpressurised and is now pressurised then that is a different story (i.e. you've upped the operating pressure).

CaptainCoPilot · 21-01-2021 6:20pm

Its a tricky one OP.

If you could describe the old heating setup you had that would help. Had you tanks in the attic that you know of?

To me it sounds likely that you had an open vented system in your old setup where a minor leak would not have been noticeable. A traditional open vented system tops itself up. A combi boiler can only be installed on a sealed (pressurised system).

This is a risk when installing a combi boiler on an old system - it may highlight leaks you were previously unaware of. Your plumber should have made you aware of this risk when quoting you the job.

The leak is likely pre-existing and not his fault, and its not really his obligation to fix that leak, wherever it is, as part of his job scope to install a combi boiler to pre existing pipework, but he should have advised you of the risk before proceeding with the job.

If you know someone with a thermal imaging camera, even one that connects to a smartphone, you may have some success finding the leak.

K.Flyer · 21-01-2021 8:26pm

As long as whatever the installer worked on is not leaking / faulty, he is not liable.
If before the new boiler was fitted you had a low pressure gravity fed system you may have a very slight to no leak. After the new boiler was installed system is now dealing with up to 1.5 bar which could be straining weak connections.
How quick you can find it depends on a number of things, moreso how you the heating has been plumbed.
If pressure is dropping from 1.5 to zero in 24 - 48 hours you will soon see a stain on your ceiling if it's anywhere upstairs.
If downstairs is old timber flooring you might be able to remove the sections near the radiators to check for leaks there.

Mick Shrimpton · 21-01-2021 8:55pm

I have almost this exact same issue with a Baxi Neta-tec combi boiler. I have to top it up most mornings these days. Only difference is that it was installed with a full brand new heating system 7 years ago.

It only happens on very cold mornings.

When the system is on, the pressure doesn't move at all so it's definitely not a leak.

The next thing we're going to try is replace the pressure relief valve... I was told that once that has been activated even once, it's a good idea to change it, maybe someone here can say if that's a good idea? Maybe it only develops the fault in really cold weather.

JCDUB · 21-01-2021 8:59pm

Thanks for the replies.

As far as I'm aware it is a gravity fed system. The big tank in the attic has a smaller tank beside it to "top up the system" beside it, according to a previous plumber.

The old boiler was an ancient Baxi one that goes in the fireplace and doubled as a horrible gas fire too.

I have been keeping an eye and an ear out for any staining etc, but have seen nothing yet.

I think it may be time to start pulling up floorboards to see if there's anything going on below. I might call a leak finder and see how much they quote me too.

I can take photos of the tank, boiler etc if that would help?

Thanks again.

JCDUB · 21-01-2021 9:02pm

Mick Shrimpton wrote: »

When the system is on, the pressure doesn't move at all so it's definitely not a leak.

This seems to be the same with my system. I haven't noticed the pressure dropping while it is running. It's usually first thing in the morning that I need to top it up.

John.G · 21-01-2021 9:33pm

If the small tank known as a feed and expansion tank or F&E tank is still in use WITH a top up system then it can only work one way and one way only, there must be a non return valve in the cold feed to the system which closes when you top up your system ( and the original vent is blanked) and stayes shut while the pressure increases a little when the system heats up. This method is known as a semi sealed system but has no top up.....the F&E tank will keep it topped up, the cold pressure will never be higher than 0.3 to 0.4 bar (static head) and the hot pressure, depending on expansion vessel capacity and pre charge pressure, only 0.75 to 1 bar. far more forgiving than the fully pressurised system. There are several of these systems around me here and work very well as long as the boiler pressure switch is happy or converted to a low pressure system, K.Flyer knows all that stuff.

The first thing to find out is whether the F&E tank is still in use as described above, and if so, why do you have a external top up system, in any case, even if (if fitted) the NRV is leaking back to the F&E tank, you should still see 0.3/0.4 bar on the boiler gauge all the time with boiler cold or hot.

I have never heard of a semi pressurised system with a external top up as it makes no sense.

K.Flyer · 21-01-2021 10:11pm

John.G wrote: »

I have never heard of a semi pressurised system with a external top up as it makes no sense.

It doesn't, but that's exactly the same problem I came across on a system, which coincidentally was fitted with a Glowworm

youtheman · 21-01-2021 11:17pm

K.Flyer wrote: »

It doesn't, but that's exactly the same problem I came across on a system, which coincidentally was fitted with a Glowworm

My house was built in 1990. Non pressurised system, header tank in attic with expansion loop into tank. About 15 years later the boiler needed replacing. Plumber didn't want to pressurise the system. So installed a condensing boiler that was designed to be pressurised, but installed it non pressurised. Installed NRV on supply from header tank in attic, removed expansion loop. System has expansion vessel and pressure relief valve. No top up loop. Low pressure switch obviously bypassed as pressure gauge is always at zero. System works fine.

John.G · 21-01-2021 11:58pm

There were lots of houses around me converted to N.gas when it became available around here, the majority were done by G.gais I think and all use the semi sealed system with great success, however the OPs boiler is indicating pressure which is apparently changing so will have to get this checked out.

K.Flyer · 22-01-2021 2:20pm

Both of those scenarios are perfectly acceptable given that there is an adequate Permanent supply of water to the heating system.

JCDUB · 22-01-2021 3:35pm

John.G wrote: »

If the small tank known as a feed and expansion tank or F&E tank is still in use WITH a top up system then it can only work one way and one way only, there must be a non return valve in the cold feed to the system which closes when you top up your system ( and the original vent is blanked) and stayes shut while the pressure increases a little when the system heats up. This method is known as a semi sealed system but has no top up.....the F&E tank will keep it topped up, the cold pressure will never be higher than 0.3 to 0.4 bar (static head) and the hot pressure, depending on expansion vessel capacity and pre charge pressure, only 0.75 to 1 bar. far more forgiving than the fully pressurised system. There are several of these systems around me here and work very well as long as the boiler pressure switch is happy or converted to a low pressure system, K.Flyer knows all that stuff.

The first thing to find out is whether the F&E tank is still in use as described above, and if so, why do you have a external top up system, in any case, even if (if fitted) the NRV is leaking back to the F&E tank, you should still see 0.3/0.4 bar on the boiler gauge all the time with boiler cold or hot.

I have never heard of a semi pressurised system with a external top up as it makes no sense.

Ok, I'm sorry, you've lost me here completely. I literally haven't a clue what this means.

Thanks for the reply, I appreciate it.
I think my only option is to either call the plumber who fitted the boiler and see what he suggests, or call another plumber.

In fairness I was happy with the installers work, apart from him not telling me this may become an issue.

At this stage I hope it's just a minor leak. Some of the replies above have frightened me a bit!

jimmycrackcorm · 22-01-2021 3:56pm

youtheman wrote: »

My house was built in 1990. Non pressurised system, header tank in attic with expansion loop into tank. About 15 years later the boiler needed replacing. Plumber didn't want to pressurise the system. So installed a condensing boiler that was designed to be pressurised, but installed it non pressurised. Installed NRV on supply from header tank in attic, removed expansion loop. System has expansion vessel and pressure relief valve. No top up loop. Low pressure switch obviously bypassed as pressure gauge is always at zero. System works fine.

Jumping in about this. My ideal classic boiler installed 20 years ago always shows the pressure gauge just working slightly above the bottom. Always wondered if there was a problem or is this the explanation?

I believe it also has an expansion vessel, and when I took off the roads last year to hose out the sludge, in didn't need to do anything to refill them.

22-01-2021 5:17pm

We replaced our 23 year old non pressurized boiler last year with a pressurized system and every 2-3 weeks we have to top up the system as the pressure very slowly drops but if we haven't had the heating on, the pressure doesn't drop.
We were told there could be a small leak somewhere. We can't find any leak anywhere, so it must be under the floor. I don't know if it is worth the effort chasing what seems to be a minor leak somewhere inaccessible.

John.G · 22-01-2021 5:36pm

JCDUB wrote: »

Ok, I'm sorry, you've lost me here completely. I literally haven't a clue what this means.

Thanks for the reply, I appreciate it.
I think my only option is to either call the plumber who fitted the boiler and see what he suggests, or call another plumber.

In fairness I was happy with the installers work, apart from him not telling me this may become an issue.

At this stage I hope it's just a minor leak. Some of the replies above have frightened me a bit!

Is the pressure dropping right down to zero and do you top it up because the boiler won't fire up?, also after topping up the pressure has to rise when the system heats up if its a pressurised system.

K.Flyer · 22-01-2021 7:39pm

[Deleted User] wrote: »

We replaced our 23 year old non pressurized boiler last year with a pressurized system and every 2-3 weeks we have to top up the system as the pressure very slowly drops but if we haven't had the heating on, the pressure doesn't drop.
We were told there could be a small leak somewhere. We can't find any leak anywhere, so it must be under the floor. I don't know if it is worth the effort chasing what seems to be a minor leak somewhere inaccessible.

It is worth it because constantly refilling a central heating system with fresh water will do more harm than good and could cost you more in the long run.
If a good attempt has been made to find the leak at least try a leak sealing treatment rather than ignore it.

JCDUB · 23-01-2021 10:38am

John.G wrote: »

Is the pressure dropping right down to zero and do you top it up because the boiler won't fire up?, also after topping up the pressure has to rise when the system heats up if its a pressurised system.

No, it doesn't quite drop to zero. About half a bar. (See attached photo.)
Yes, we have to top it up before the boiler will fire up.

John.G · 23-01-2021 12:28pm

OK, go up to the attic and see if the small tank is full/overflowing or even more than 3/4 full, you will see a plastic ball floating on top of the water, if this is more than ~ "1/2" submerged in the water or more then you have found your problem (non return valve leaking). If no water in the tank or water level normal then I'm afraid you havn't.

um7y1h83ge06nx · 23-01-2021 3:34pm

I've been having a similar issue and I went to check my expansion vessel with a pressure gauge and water came out of it immediately.

I presume this means the vessel is totally fcuked and needs to be replaced rather then just pumped back up?

John.G · 23-01-2021 3:43pm

Correct, renew the E.vessel, check/adjust air pressure @1 bar before installing and then pressureise (water side) to 1.5 bar with cold boiler/system.

um7y1h83ge06nx · 23-01-2021 3:49pm

John.G wrote: »

Correct, renew the E.vessel, check/adjust air pressure @1 bar before installing and then pressureise (water side) to 1.5 bar with cold boiler/system.

Perfect, thank you for the response. Think I'll leave it in the hands of our plumber, couldn't be listening to the wife if I messed it up.

JCDUB · 23-01-2021 5:04pm

John.G wrote: »

OK, go up to the attic and see if the small tank is full/overflowing or even more than 3/4 full, you will see a plastic ball floating on top of the water, if this is more than ~ "1/2" submerged in the water or more then you have found your problem (non return valve leaking). If no water in the tank or water level normal then I'm afraid you havn't.

I went up and had a look and the small tank is no longer there any more. Obviously the plumber took it out when he was fitting the boiler.

He just blanked the pipe between the big tank and little one.

Thanks for the advice, the search continues.

23-01-2021 5:53pm

Kalyke wrote: »

I had a Baxi Combi installed recently. A couple of weeks after installation I bled a radiator, the pressure dropped and the boiler stopped working. I called (and called and called) the installer for help but he never replied. I found a valve in the hotpress that pressurized the system. I then had a local plumber have a look at my system. The "expansion" tank was disconnected. That is no input or output. He says he can sort it for me. If he does is my Baxi warranty voided? If so, what is my next step as the installer will not reply. (He is RGII registered) Can I complain to Baxi or RGI? Thanks.
Edit....Should I start a new thread?

Would make things easier.

JCDUB · 26-01-2021 4:31pm

So, an update.

The plumber came today and rather than pulling up floorboards looking for a leak that we may not find, he said the best course of action would be to fit an Automatic Filling Valve.

So, he has done this.

This valve tops up the system when the pressure drops, according to him.

As long as the problem is fixed, I'm fine with this, although I am slightly worried about the previous post that said constantly topping up the system will corrode it from the inside out. Should I be worried?

As an aside, he charged €150 for this, sound about right?

CoBo55 · 26-01-2021 4:57pm

JCDUB wrote: »

So, an update.

The plumber came today and rather than pulling up floorboards looking for a leak that we may not find, he said the best course of action would be to fit an Automatic Filling Valve.

So, he has done this.

This valve tops up the system when the pressure drops, according to him.

As long as the problem is fixed, I'm fine with this, although I am slightly worried about the previous post that said constantly topping up the system will corrode it from the inside out. Should I be worried?

As an aside, he charged €150 for this, sound about right?

No way I'd accept this. That's curing the symptoms not the disease. I'm on my second automatic filling valve and I leave this one turned off as it was fine for about 6 months and then it went nuts and overpressured the system bursting the expansion vessel and lifting the pressure relief valve at the boiler. I hate them with a passion.

K.Flyer · 26-01-2021 5:46pm

JCDUB wrote: »

So, an update.

The plumber came today and rather than pulling up floorboards looking for a leak that we may not find, he said the best course of action would be to fit an Automatic Filling Valve.

So, he has done this.

This valve tops up the system when the pressure drops, according to him.

As long as the problem is fixed, I'm fine with this, although I am slightly worried about the previous post that said constantly topping up the system will corrode it from the inside out. Should I be worried?

As an aside, he charged €150 for this, sound about right?

So he hasn't actually rectified the issue of the heating system loosing water. All he has done is saved you the effort of refilling the system when the pressure drops. Did he even attempt a leak seal treatment?

As per my earlier post, it is not good for a heating system to be constantly topped up with fresh water.
The leak still exists and could be doing unseen damage to your property. What happens if the leak worsens, then that filling valve will just keep feeding water into the system probably doing further damage and by the time you find out it could become a very expensive shortcut.

Sleeper12 · 26-01-2021 6:37pm

I'd imagine having fresh water in your system will void the manufacturer warranty on the boiler?

New combi boiler fitted, system losing pressure. What to do?

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