My gas combi's sealed system pressure drops from 1.0 to about 0.5 bar every
few weeks. It seems to stick at 0.5, but I've not left it long enough to be
sure. A few seconds on the loop valve and it's back to pressure - so at most a
pint or two of water.

I can't see anything obvious at and around the rads and pipework, but did come
across an encrusted main water inlet valve/unions on the boiler. This was an
issue soon after the boiler was installed, and I've only just noticed it now.
There's no sign of dripping water though. Could this be the cause of the
pressure loss?

--
Cheers, Rob

On 29/08/2020 18:50, RJH wrote:
My gas combi's sealed system pressure drops from 1.0 to about 0.5 bar every
few weeks. It seems to stick at 0.5, but I've not left it long enough to be
sure. A few seconds on the loop valve and it's back to pressure - so at most a
pint or two of water.

I can't see anything obvious at and around the rads and pipework, but did come
across an encrusted main water inlet valve/unions on the boiler. This was an
issue soon after the boiler was installed, and I've only just noticed it now.
There's no sign of dripping water though. Could this be the cause of the
pressure loss?


Sound like the expansion vessel needs repressurizing, or maybe replacing
as it has a punctured diaphram.

After serious thinking RJH wrote :
My gas combi's sealed system pressure drops from 1.0 to about 0.5 bar every
few weeks. It seems to stick at 0.5, but I've not left it long enough to be
sure. A few seconds on the loop valve and it's back to pressure - so at most
a
pint or two of water.

Check the PRV (Pressure Release Valve), usually the exit pipe is
outside - put a plastic bag tight over the end, with an elastic band.
If that collect some water, that's where it is being lost.

Does the pressure increase, when the boiler is burning? Could be that
the expansion vessel has no air in it, so as the pressure rises, it is
forced out the PRV.

On 29/08/2020 19:06, Harry Bloomfield wrote:
After serious thinking RJH wrote :
My gas combi's sealed system pressure drops from 1.0 to about 0.5 bar
every
few weeks. It seems to stick at 0.5, but I've not left it long enough
to be
sure. A few seconds on the loop valve and it's back to pressure - so
at most a
pint or two of water.

Check the PRV (Pressure Release Valve), usually the exit pipe is outside
- put a plastic bag tight over the end, with an elastic band. If that
collect some water, that's where it is being lost.

Agreed

Does the pressure increase, when the boiler is burning? Could be that
the expansion vessel has no air in it, so as the pressure rises, it is
forced out the PRV.

Agreed. If it repressurises quickly that may be an indicator of a failed
expansion vessel. Often a PITA to replace, easier to add an external one
if you have basic plumbing skills. It doesn't have to be right next to
the boiler.

If the pressure relief valve has been weeping there may be erosion
damage on the seat, so that it always leaks after the primary problem is
fixed. They are usually a generic product, available from BES rather
cheaper than the manufacturer's version. You just have to make sure you
have the right size and gender. Not usually too difficult to replace.

On 29 Aug 2020 at 22:21:05 BST, "newshound"
wrote:

On 29/08/2020 19:06, Harry Bloomfield wrote:
After serious thinking RJH wrote :
My gas combi's sealed system pressure drops from 1.0 to about 0.5 bar
every
few weeks. It seems to stick at 0.5, but I've not left it long enough
to be
sure. A few seconds on the loop valve and it's back to pressure - so
at most a
pint or two of water.

Check the PRV (Pressure Release Valve), usually the exit pipe is outside
- put a plastic bag tight over the end, with an elastic band. If that
collect some water, that's where it is being lost.

Agreed

Done - I'll check when it's next on, thanks.



Does the pressure increase, when the boiler is burning? Could be that
the expansion vessel has no air in it, so as the pressure rises, it is
forced out the PRV.

Yes, it usually goes up 0.5 bar or so.


Agreed. If it repressurises quickly that may be an indicator of a failed
expansion vessel. Often a PITA to replace, easier to add an external one
if you have basic plumbing skills. It doesn't have to be right next to
the boiler.

If the pressure relief valve has been weeping there may be erosion
damage on the seat, so that it always leaks after the primary problem is
fixed. They are usually a generic product, available from BES rather
cheaper than the manufacturer's version. You just have to make sure you
have the right size and gender. Not usually too difficult to replace.

Thanks, I'll take a look.

--
Cheers, Rob

On Saturday, 29 August 2020 18:50:11 UTC+1, RJH wrote:
My gas combi's sealed system pressure drops from 1.0 to about 0.5 bar every
few weeks. It seems to stick at 0.5, but I've not left it long enough to be
sure. A few seconds on the loop valve and it's back to pressure - so at most a
pint or two of water.

I can't see anything obvious at and around the rads and pipework, but did come
across an encrusted main water inlet valve/unions on the boiler. This was an
issue soon after the boiler was installed, and I've only just noticed it now.
There's no sign of dripping water though. Could this be the cause of the
pressure loss?

I don't know whether it's the whatsit bottle or the valve, but encrustation does indicate a leak over time.


NT

On 31 Aug 2020 at 21:52:56 BST, "
wrote:

On Saturday, 29 August 2020 18:50:11 UTC+1, RJH wrote:
My gas combi's sealed system pressure drops from 1.0 to about 0.5 bar every
few weeks. It seems to stick at 0.5, but I've not left it long enough to be
sure. A few seconds on the loop valve and it's back to pressure - so at
most a
pint or two of water.

I can't see anything obvious at and around the rads and pipework, but did
come
across an encrusted main water inlet valve/unions on the boiler. This was an
issue soon after the boiler was installed, and I've only just noticed it
now.
There's no sign of dripping water though. Could this be the cause of the
pressure loss?

I don't know whether it's the whatsit bottle or the valve, but encrustation
does indicate a leak over time.


Don't think it's either. The expansion vessel is at 0.6 bar, with a specified
range of 0.5 to 0.75. Nothing in the plastic bag on the overflow (after a
couple of showers and a few hours of heating).

While in, I had a closer look at the fitting and I'm pretty sure it's
historic, and no sign of any drips or leaks. The only other thing was the
condensate trap water looked very murky. That'll need cleaning at some point,
but it isn't the cause of the pressure drop.

So, under the floorboards for me. Joy.

--
Cheers, Rob

On Tuesday, 1 September 2020 18:34:05 UTC+1, RJH wrote:
On 31 Aug 2020 at 21:52:56 BST, "tabbypurr wrote:
On Saturday, 29 August 2020 18:50:11 UTC+1, RJH wrote:
My gas combi's sealed system pressure drops from 1.0 to about 0.5 bar every
few weeks. It seems to stick at 0.5, but I've not left it long enough to be
sure. A few seconds on the loop valve and it's back to pressure - so at
most a
pint or two of water.

I can't see anything obvious at and around the rads and pipework, but did
come
across an encrusted main water inlet valve/unions on the boiler. This was an
issue soon after the boiler was installed, and I've only just noticed it
now.
There's no sign of dripping water though. Could this be the cause of the
pressure loss?

I don't know whether it's the whatsit bottle or the valve, but encrustation
does indicate a leak over time.


Don't think it's either. The expansion vessel is at 0.6 bar, with a specified
range of 0.5 to 0.75. Nothing in the plastic bag on the overflow (after a
couple of showers and a few hours of heating).

While in, I had a closer look at the fitting and I'm pretty sure it's
historic, and no sign of any drips or leaks. The only other thing was the
condensate trap water looked very murky. That'll need cleaning at some point,
but it isn't the cause of the pressure drop.

So, under the floorboards for me. Joy.

Well, at least it's not time to dig up the concrete floor.


NT