Central heating issue

[Langers_2011]

I’ve got a central heating system that’s losing pressure.
The expansion vessel was repressurised to 1.5 and held that pressure. I’ve replace the prv to a brand new one also.
I’ve turned the boiler off and put the condensate into it and no water has come out.
No water is coming out of the prv drain pipe.
There are no visible leaks but I’m still losing pressure. Roughly 0.5bar every hour or so.
I have a Worcester 30cdi

 

[Exedon]

If nothing out of prv or condensate waste and no obvious leaks on boiler , and you have re pressured a number of times look round system.
Rad valves are a favourite.
Any buried pipework?

 

[Langers_2011]

If nothing out of prv or condensate waste and no obvious leaks on boiler , and you have re pressured a number of times look round system.
Rad valves are a favourite.
Any buried pipework?

There are definitely no leaks from rads or from pipework. I can see all the pipework apart from a couple small sections, but by now there would be stacks of water.

 

[Exedon]

If that's a system boiler
Cylinder coil next suspect.

 

[CountryFan]

Pressurise the system to approx 2.5 bar, Isolate the boiler flow and return and unisolate the boiler after a period of 8 hours. If it drops before that it's the boiler, if it drops after that, it's the system.

 

[Langers_2011]

If that's a system boiler
Cylinder coil next suspect.

I don’t have one of those.

 

[Langers_2011]

Pressurise the system to approx 2.5 bar, Isolate the boiler flow and return and unisolate the boiler after a period of 8 hours. If it drops before that it's the boiler, if it drops after that, it's the system.

Thanks.
Where would it be leaking from the boiler. I have no water anywhere, same with the system. It’s really not making sense. Would a bottle valve trap inside the boiler that’s failed (not leaking water) cause any issues like this?

 

[terryplumb]

Do you lose pressure when the boiler is cold ( not been used for a few hours )and not in use at all for domestic hot water or central heating ?

 

[Langers_2011]

Do you lose pressure when the boiler is cold ( not been used for a few hours )and not in use at all for domestic hot water or central heating ?

I’m pretty sure we do as it’s not been used and ends up empty, I can double check this.
Only things I haven’t replaced is the expansion, but again this let me pressurise it to 1.5 and the bottle trap.
The boiler is just heating. It has 3 zones, but two have not been active the last few weeks and are on those electronic isolation box things.

 

[Langers_2011]

Just check and pressure back down to near 0, last filled it up around 5.30.
There is zero water anywhere, both overflows are dry as a bone too. At an absolute loss

 

[denso13]

Just check and pressure back down to near 0, last filled it up around 5.30.
There is zero water anywhere, both overflows are dry as a bone too. At an absolute loss

I'd try this.

Pressurise the system to approx 2.5 bar, Isolate the boiler flow and return and unisolate the boiler after a period of 8 hours. If it drops before that it's the boiler, if it drops after that, it's the system.

 

[Langers_2011]

I'd try this.

I’ll do it over night and see what happens

 

[terryplumb]

If you are losing pressure when the boiler isn't being used ,and nothing is coming out the boiler,it's condensate pipe,or the PRV's discharge pipe, that's indicative of a leak on the system. Is there any heating pipework buried in concrete flooring ,or a void under the ground floor?