Glow Worm Boiler - Pressure Increasing

junglejuiced

Hi,

I've got a Glow Worm boiler that has slowly been increasing in pressure over the last few weeks when off. I've had a plumber round to look at it and he said the expansion vessel was dead. Water came out of the valve when he pressed it. He's replaced the vessel and checked that the filling loop is not passing any water and it's not but it's still gaining pressure. I'm not sure what else it could be. Also, the boiler is just for the central heating and does no hot water as I have a separate water heater for that so I'm stumped as to what could be causing the pressure increase.

Any ideas?

Thanks

Ruski

If the filling loop is still connected - disconnect it and then wait and see.

Russ

junglejuiced

Hi Russ,

Thanks for the reply. I disconnected the filling loop last night just to make sure it wasn't leaking and it still went up overnight. So strange. Do pressures in systems fluctuate much when not in use by a small amount?

Alex

Ruski

If it's a heat only boiler - and not connected to your cylinder in any way then I'm stumped tbh!

When you say pressure - what gauge are you looking at? CH pressure elsewhere on the system? Gauge on the boiler itself?

What boiler model is it?

Pressure will drop a small amount, but not by a couple of bar - which it sounds like you are describing?

Russ

junglejuiced

The pressure I'm looking at is what's on the digital read out on the boiler. It's a Glow Worm 18SXI and apart from the filler loop (which is disconnected) has no other connection to the mains.

The pressure is steadily increasing by about 0.1 bar per 12 hours but consistently and it's been turned off for a month now as it's summer.

I'm stumped as well and the plumber I spoke with is not sure either. Could it be the pressure sensor?

Le_Kirk

It's a sealed system, the only way to increase pressure is to add water through the connecting loop. You have a separate system for hot water, so there is not part of the system that goes through the hot water cylinder that might have a leak (although if all that is true, it tends to decrease not increase). When I fire my boiler the pressure increases slightly with temperature increase. Is there some external influence on the temperature of the water in the system, e.g. ambient temperature where the pipes go (loft for example) or hot water cylinder coupled with a slightly open three-port valve (if indeed you have such a system. Otherwise I am similarly stumped!

junglejuiced

Yeah, it's a sealed system and the water heater is completely separate, the pipes don't even run close together. The pipes do run up to the attic which has been converted and is definitely warmer than where the boiler is which is essentially below ground in a half basement but not sure that would be enough to increase water pressure through an ambient change over the course of the system would it?

Could it be the pressure sensor and do you know if I can buy an independent device to check the pressure on the system?

Thanks

Ruski

OK, lets talk DHW - what is your setup for that, and what makes you think that the boiler is not responsible for supplying your hot water?

What's in the airing cupboard? Any two/three port valves in there? Is it a pressurised DHW system?

Photo's would also speak a million words...

Russ

junglejuiced

Hi Russ,

Thanks for taking the time to reply. The hot water comes from a gas water heater (Britony) which is a small on the wall unit in my downstair toilet. I'm not at home at the moment so can't take any pictures but from memory it seems to be a fairly straight forward pipe in pipe out system and can't recall any port valves. Although it does have a water pressure reducer as my mains water pressure is extremely high in my area so it's used to slow the rate of water going into the system I think.

Thanks

Alex

alan.t

Try ringing Glowworms technical dept and speaking to them, they may be able to help diagnose the problem

Ruski

Okay - that rules out the DHW side as long as you're sure the two aren't linked in any bizarre way (and I would hope not!)

It's only a very minor possibility but it could be expanding air in the system - I presume that you and your plumber have already bled ALL the radiators (especially the top floor ones as most air will accumulate there) ?

Russ