Weird boiler pressure issue - keeps dropping.

[VincentHanna]

We have a house built in the 80's but the previous owners did a complete extension refurb and put a viessmann combi boiler in.

The old part of the house has 8 radiators. The kitchen and new extension part has underfloor heating. It's worked fine for 2 ½ years and I even had it serviced less than year ago just to be on the safe side.

A few nights ago I noticed the boiler sounded different when firing up, so I checked and the pressure was low - nearly zero.

I filled it back to 1 bar and assumed I had solved it.

But the pressure now appears to drop quite rapidly (within 8 hours) and goes back to 0!

I've had to re-fill it 3 times in 24 hours. Usually once or twice a year would be enough.

I've checked every radiator in the house and looked for damp walls and can't see anything.

It's possible the leak is with the underfloor heating but that is impossible to get at as it's under tiles in the kitchen.

I know I will need a professional to look in to this, but where else could this water possibly be draining out of? And wouldn't it be really obvious if it's losing pressure that quickly and presumably leaking water somewhere?

 

[mattyfez]

I can give a little advice as I've hopefully fixed my leak..
It was a bleed nipple on a radiator not quite tight enough... It was barely wet to the touch though it was so small.

But I'm losing pressure more slowly than you... I'm topping up pressure every few days. So I'll know in a few days if that was it.


You could look on the exterior wall the other side of the boiler.. Not the main plasic vent but there should be a copper overflow pipe (that's not the proper name of it, which I can't remember) that's kinda curled round.

If that ever gets wet /drips coming out.. It's a problem inside the boiler. It will be very subtle though.. You may need to tape a little plastic bag to it to see if it catches any water over time

There are a couple of things internal to the boiler that can cause pressure loss other than that.

If you've checked the pipe work as best you can, there is one thing you can do without the help of a pro... But it will mean the boiler being unusable for a day or so...

... Google how to isolate a boiler. Essentially your going to shut the boiler valves off from all the water pipes.

I'm not sure if you need to keep the boiler running as normal like this.. You'll have to look it up.

If it continues to lose pressure then the fault lies within the boiler..
If it maintains pressure it means there must be a leak in the pipework somewhere.

Don't forget when you do get it fixed the water in the system won't have any inhibitor fluid in it, so it's important to add that back in to keep water in the pipes in better condition.

 

[henry hoov3r]

The underfloor heating system should have a manifold somewhere so that should be relatively easy to isolate from the main system. Another possibility although somewhat unlikely is the boilers AAV letting by. Its very common but losing that amount of pressure that quickly it would usually be dripping out the bottom of the boiler. Also if you do decide to isolate the boiler be careful with the isolation valves they can be a bit brittle.

 

[Rob_B]

It sounds like a leak, we just had the same with a joiner putting a nail through a pipe, there was no real amount of water but one of the skirting boards just felt a teeny bit damp but not wet.

The water must be going somewhere. Do you have access to a thermal camera? Fire the heating up and walk along and see if any walls or floors are getting hot in the wrong place.

 

[b0rn2sk8]

Assuming it’s a pressurised system, which it sounds like it is, the system will have an over pressure valve which it can dump water out of.

This usually has a turn dish on it so you can see the water flowing. It could well just be a failure there.

There are lots of different failure points, if there is no obvious water leak which there will be if it’s losing pressure in 8 hours, it’s time to call in a trade to fix it.

 

[doopydug]

Have you had any work done in the house recently - fitted kitchen / bathroom or even a joiner doing some works?

 

[darael]

The last time I had this kind of problem, it turned out to be the expansion vessel which had gone.

 

[VincentHanna]

Have you had any work done in the house recently - fitted kitchen / bathroom or even a joiner doing some works?

None whatsoever

 

[Mason-]

Sounds like a leak. Any of your pipes buried in concrete? Also when you added water back to the system did you bleed the rads?

 

[wesimmo]

I recently had my boiler replaced because the diverter valve (?) had gone.

I also lost pressure regularly, but I also had other symptoms. Using hot water would heat the central heating system too. Or putting the heating on would heat the hot water system even if turning hot water taps on wouldn't cause the boiler to fire up.

 

[VincentHanna]

Another question then. The pipes from the boiler are all behind a fitted kitchen cabinet

Would I be expected to remove all this, so a gas technician can access everything? Or would they do that?

 

[wesimmo]

I'd ask whoever is coming out.

I struck absolute gold with my boiler man, nothing was too much trouble, even to the point of nipping to screwfix to get parts and refit some pipework that exploded in the down stack column when a re-pressurised the system and found that there had been no/little solder on the pipes when fitted 20 odd years ago. No charge for that either.

On the other hand, I've had bathroom and kitchen fitters in the last couple of years who I'd shoot if I ever saw them again.

 

[henry hoov3r]

I recently had my boiler replaced because the diverter valve (?) had gone.

I also lost pressure regularly, but I also had other symptoms. Using hot water would heat the central heating system too. Or putting the heating on would heat the hot water system even if turning hot water taps on wouldn't cause the boiler to fire up.

Seems a bit extreme to change the boiler because it needed a new divertor.

 

[wesimmo]

Seems a bit extreme to change the boiler because it needed a new divertor.

It was 21 years old anyway, I had to go into the garage to turn it on or off or play with the timer, which was one of the old dial types...

New part was £4/500 or a new efficient boiler for £2k.

 

[henry hoov3r]

It was 21 years old anyway, I had to go into the garage to turn it on or off or play with the timer, which was one of the old dial types...

New part was £4/500 or a new efficient boiler for £2k.

21 years old fair enough! If it was a Worcester CDI which is from that era they are a pig to change.

 

[SpellowHouse]

We have a house built in the 80's but the previous owners did a complete extension refurb and put a viessmann combi boiler in.

The old part of the house has 8 radiators. The kitchen and new extension part has underfloor heating. It's worked fine for 2 ½ years and I even had it serviced less than year ago just to be on the safe side.

A few nights ago I noticed the boiler sounded different when firing up, so I checked and the pressure was low - nearly zero.

I filled it back to 1 bar and assumed I had solved it.

But the pressure now appears to drop quite rapidly (within 8 hours) and goes back to 0!

I've had to re-fill it 3 times in 24 hours. Usually once or twice a year would be enough.

I've checked every radiator in the house and looked for damp walls and can't see anything.

It's possible the leak is with the underfloor heating but that is impossible to get at as it's under tiles in the kitchen.

I know I will need a professional to look in to this, but where else could this water possibly be draining out of? And wouldn't it be really obvious if it's losing pressure that quickly and presumably leaking water somewhere?

If the pressure has dropped to zero, then it's very possible air has got in the system, and it can take a little time to get it out again. I would keep on filling it for a few more days and see if it stabilises. The air is released by the boiler itself, but it takes time for it to work its way out of the system.

It's unlikely to be a leak because you would be aware of that, even if it was in the floor. It is most likely that the problem was initially caused by a slow leak that is just evaporating away. I am afraid it is very difficult to find leaks like. It's a question of searching round to find slight hints of damp. Green on the positive pressure side and white on the negative.

 

[Werewolf]

The last time I had this kind of problem, it turned out to be the expansion vessel which had gone.

Same here.

It kept getting to shorter and shorter periods between topping up.

 

[Countcussy]

Expansion vessel is always the next thing to check, if you cant see a leak.
Expansion vessel failure, means nowhere for the water to expand at it heats up.
This causes the system to over pressurise, and safety valves dump the water either outside, or to waste. Problem is, depending on the system, you cannot always see this happening.
Also worth noting that every time you "Top up", you are diluting the inhibitor in the system. Make sure you top that up as well.

The air is released by the boiler itself, but it takes time for it to work its way out of the system.

What ??

 

[mattyfez]

Expansion vessel is always the next thing to check, if you cant see a leak.
Expansion vessel failure, means nowhere for the water to expand at it heats up.
This causes the system to over pressurise, and safety valves dump the water either outside, or to waste. Problem is, depending on the system, you cannot always see this happening.
Also worth noting that every time you "Top up", you are diluting the inhibitor in the system. Make sure you top that up as well.

Also this!

Once its sorted, you'll have been topping it up with so much 'fresh' water from the mains water via the filling loop that:

A) That fresh water will be quite oxygenated (think if you fill a pint glass up from a tap, fast, it might look slightly cloudy due to all the tiny air bubbles in it, it will settle down in a few secs, but it can't do that in a sealed system) so you may have to bleed the radiators again, as all those almost microscopic air bubbles will combine to form air pockets in the pipe work.

B) Topping up a lot will also dilute any existing inhibitor fluid, so you'll need to re-dose it back up with inhibitor again, and possibly do a small final bleed on the radiators.

 

[mattyfez]

The air is released by the boiler itself, but it takes time for it to work its way out of the system.

Not sure about that? the boiler will dump water if it becomes overpressurized... either straight out of the bottom of the boiler, onto the carpet, or through ones of these, outside, depending on the fault:

https://external-preview.redd.it/UhAGmRFXD4yPCU-zT6kxVcj0Raas8SIFHn4Yvqqgdb4.jpg?width=640&crop=smart&auto=webp&s=7a7f3b67e6edddc66b19246330028a4b53df7444

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