Worcester Greenstar 32CDi combi boiler keeps losing pressure fast - no leak

[Namo Amituofo]

Hi all

I hope someone can help me debug this mysterious issue.

5 year old Worcester Greenstar 32CDi boiler started losing pressure fast. Refilled to 1.5 bar last night, and by this morning it was down to 0 again. This happened multiple times. Last week it was serviced by a gas engineer (the pressure issue happened before the service) but he didn't identify any obvious issue.

CT and HW both work fine, even when the pressure gauge is at 0. That said, the boiler throws a slight clunking noise when CT or HW is on at 0 pressure. No error codes.

When I refill the boiler, the pressure steady reaches 1.5 - so don't think the gauge is faulty.

No leak near any radiators, or any wet patches I can identify on walls and ceilings. No drip or wet patches under the boiler either.

Given I'd refilled the boiler at least 5 times in the past few days, if this was a leak, there MUST be a lot of water leaked out and I cannot find any leak in the house.

Anyone can shed light I'd be really appreciated.

Namo Amituofo

 

[CBW]

Check the copper pipe from under the boiler, usually terminates outside - if nothing else visible likely this or the main heat exchanger is passing - if the copper pipe is ok,are you able to check the plastic white pipe when boiler not in use? Check that the pressure isn’t rising when heating is on.

 

[Namo Amituofo]

i found a little drip in the drain pipe outside the house - put a 250ml glass jar under the pipe, and in about 1hr it was almost full.

does this suggest pressure release valve at fault?

 

[CBW]

i found a little drip in the drain pipe outside the house - put a 250ml glass jar under the pipe, and in about 1hr it was almost full.

does this suggest pressure release valve at fault?

What is connected to the drain pipe? Sounds more like condensate pipe.

 

[Namo Amituofo]

it is most likely the condensation pipe. drips about 250ml per hr. does this make diagnosis easier?

 

[CBW]

drips about 250ml per hr. does this make diagnosis easier?

Not necessarily, does it drip without being in use?

 

[Namo Amituofo]

It drips when CH or HW is on, and this corresponds to when water pressure loss happens. Also I’ve noticed water pressure holds OK when CH and HW is off

 

[CBW]

It drips when CH or HW is on, and this corresponds to when water pressure loss happens.

That’s fine, as it’s condensing as it should.

Also I’ve noticed water pressure holds OK when CH and HW is off

Then it can’t be the main heat exchanger or unlikely to be the pressure relief valve. Could be an expansion related issue. Can you see your pressure gauge? If yes, next time the heating has been on for 15 minutes have a look, see if it’s high.

 

[Namo Amituofo]

Pressure gauge does not move when boiler is on. I don’t think it’s normal for condensation drip to accumulate to 250ml per hour?

 

[MagicDoughnut]

Water from the condensate does not come from your sealed central heating system, therefore it would not drop your systems pressure.

Stupid question, the water you're collecting, is it coming from a plastic pipe or copper pipe?

A boiler loosing pressure that quickly is either PRV, expansion vessel or a leak.

 

[Namo Amituofo]

There are two black painted pipes about 1 inch diameter that comes through the wall - can’t tell if they are copper or plastic though - has a metal feel to them but heavily painted black.

Could you enlighten me where does condensation water come from? It’s a lot of water I’ve collected today down that pipe.

 

[MagicDoughnut]

The copper pipe is smaller in diameter than the condensate.

The water from the condensate is just that, condensate from the boilers emissions.