Pressure Drop in Boiler

[texas_pedro]

Wondering if anyone can give some help - cut a long story short, boiler losing pressure when heating not on. Have tried a good few options (all the usual suggestions that you would normally suggest) but nothing repaired it. So, before deciding it was definitely a leak somewhere (and given no sign of leak likely underground) we decided to cap off the boiler and pressurise the pipes, with a separate pressure gauge - with the thinking being if no drop then need a new boiler, or if it does drop then a leak. We set it to around 2 bar, and it has dropped slightly to 1.8 over 24 hours, but not as much as I would have thought if it was leak. Anyone have any professional opinions on what they would expect it to drop to if it was a leak?

 

[PlumbBobBob]

sounds like you don't have a leak on your pipework the 0.2 bar drop will just be slight compression and cooling of the air over time.

 

[texas_pedro]

sounds like you don't have a leak on your pipework the 0.2 bar drop will just be slight compression and cooling of the air over time.

Thanks for the reply. As a best guess (and I appreciate several variables here) what would you think it would drop to (given the boiler loses pressure pretty quickly when heating not on) and how fast if it was a leaky pipe.

 

[Riley]

Might be good to get a GS Engineer out to have a nose in the boiler. It may not be as write off yet

 

[PlumbBobBob]

Thanks for the reply. As a best guess (and I appreciate several variables here) what would you think it would drop to (given the boiler loses pressure pretty quickly when heating not on) and how fast if it was a leaky pipe.

if the pipework were leaking i would expect it to have a greater loss than 0.2 bar possibly right down to zero or very close.

 

[texas_pedro]

if the pipework were leaking i would expect it to have a greater loss than 0.2 bar possibly right down to zero or very close.

Appreciate the reply. It's dropped a wee bit more, but nothing substantial. I'll leave it a few more days maybe just to be sure but think by the sounds of it it's not the pipe work.

 

[cr0ft]

Sorry but any drop in pressure in this test situation (after about 10 minutes) means you have a water leak. Pump it up to 10 bars and listen out for hissing. You should hear a loud hissing noise from the failed joint. At this pressure you will hear it underneath concrete floors or inside walls. This is a very controlled way to find the failed joint. Have someone ready to let off the pressure into the tester quickly if the joint does fail in style (fairly unlikely). If you don't find the joint like this eventually it is going to give up the ghost anyway so best to find it in a more controlled fashion.

Your pressure drop equates to a water loss of around 500mL in a 100L sealed system. That's less than 21mL per hour. I'm not surprised you're not seeing any water leaking. At this volume it will be evaporating away into the atmosphere.

There is no possibility this is down to air after 24 hours. Small amounts of air in pipework will quickly reach the property temperature, 10 minutes is all you need to allow for this to take place.

 

[texas_pedro]

Sorry but any drop in pressure in this test situation (after about 10 minutes) means you have a water leak. Pump it up to 10 bars and listen out for hissing. You should hear a loud hissing noise from the failed joint. At this pressure you will hear it underneath concrete floors or inside walls. This is a very controlled way to find the failed joint. Have someone ready to let off the pressure into the tester quickly if the joint does fail in style (fairly unlikely). If you don't find the joint like this eventually it is going to give up the ghost anyway so best to find it in a more controlled fashion.

Your pressure drop equates to a water loss of around 500mL in a 100L sealed system. That's less than 21mL per hour. I'm not surprised you're not seeing any water leaking. At this volume it will be evaporating away into the atmosphere.

There is no possibility this is down to air after 24 hours. Small amounts of air in pipework will quickly reach the property temperature, 10 minutes is all you need to allow for this to take place.

Cheers for the reply. As an update - the pressure did continue to drop, but very slowly. Its been 72 hours and its down to around 1.4-1.5. So we do think its a leak - however, to be 100% certain we reconnected the boiler to hot water only to see if the boiler lost pressure. It doesn't seem to be, so that looks ok. So next decision is how we go about finding it - I'll leave that up to the professionals. We do have a clause in our home insurance that covers this kind of thing so we may ask them, as the plumber didn't seem keen ripping up floorboards (nor are we!)

 

[oil gasman]

what make model of boiler do u have please

as its a sealed system maybe the expansion vessel inside ur boiler ,

the pressure relief valve pipe outside isn't leaking by any chance ??

but please don't attempt to touch it yourself get an engineer in to carry out a test for u

 

[cr0ft]

He's isolated the boiler mate so he should just be checking the pipework only.

If it's a combi don't run it on HW only without it being able to pump round the CH circuit. Combi boilers need the CH circuit open to dump any excess heat into it once HW is shut off. Running a combi on hot water uses a lot of energy and when you shut the hot water off that energy needs to go somewhere quickly.

With a simple 10 bar pressure test you will hear the leak I can promise you that!

 

[IDCHAPPY]

At 10 bar you'd hear my ar$e flapping :lol:

 

[cr0ft]

LOL do you often pressure test your arse? Actually I'm not sure I really want to know!

 

[oil gasman]

He's isolated the boiler mate so he should just be checking the pipework only.

If it's a combi don't run it on HW only without it being able to pump round the CH circuit. Combi boilers need the CH circuit open to dump any excess heat into it once HW is shut off. Running a combi on hot water uses a lot of energy and when you shut the hot water off that energy needs to go somewhere quickly.

With a simple 10 bar pressure test you will hear the leak I can promise you that!

sorry didn't realise he had completely isolated the boiler ,must read slower, lol

i wouldnt like like to be around when a fitting goes at 10 bar, one way to find a weak fitting

assume all then rads are all vented , rad valve caps removed and the spindles checked , motorised valves have been checked, around pump valves etc not leaking

wonder if there an extra external expansion vessel fitted , or maybe an aat letting by

just a thought

 

[IDCHAPPY]

My arse is good for steam rated pressure and heat... the farmer giles my not like it though

 

[texas_pedro]

We did all the usual checks before going down this route - and don't worry, I'm not touching anything. All being done by a pro.

Latest at is the pressure in pipes is still sitting at 1.4/1.5 (that's now a drop of 0.6 in 4 days). However, the boiler also seems to be slowly losing pressure as well. So not sure what to think. We're leaving both to next week to see how much further it drops. But wonder if there is both a small leak and a broken boiler. Double whammy!