Unvented system losing pressure again...

[Syd98]

Hi.
Unvented megaflo with a Worcester Bosch regular green star 18i boiler.
Megaflo 10yrs old , boiler 2years..
All worked fine for two years, until recently, system pressure dropped, local guy said it was expansion vessel and removed re fitted new vessel. System back up and running..
But lost pressure again after one heating cycle..
Tun fish was bone dry so I put a bucket on condensate drain from boiler, re topped up and fired the heating up on one more cycle.. Next morning pressure 0 roundish dry and probably a litre of water in the bucket, that was out of the boiler condensate drain, not the tun dish over pressure drain.
Help .. Any suggestions?

 

[dcawkwell]

expansion vessel has no air in.it. drain boiler check expansion vessel has about 1bar.
run boiler does pressure go up to 3 bar?

 

[Syd98]

Expansion vessel has 1bar in it, measured when off (new out of box) so per charged with 1 bar of nitrogen.
How much condensate would you expect to see discharged out of the condensate drain having boiler running for 3 hrs with HW and CH on ?
System was only running at 2bar never saw it go higher so could not have been through 3bar PRV ?
Any other suggestions..

 

[dcawkwell]

Expansion vessel has 1bar in it, measured when off (new out of box) so per charged with 1 bar of nitrogen.
How much condensate would you expect to see discharged out of the condensate drain having boiler running for 3 hrs with HW and CH on ?
System was only running at 2bar never saw it go higher so could not have been through 3bar PRV ?
Any other suggestions..

Sorry. I think I miss read.
If you have no loss from the pressure relief pipe. You have a leak
in the system somewhere.
A litre coming from the condensate is nothing special.
Most likely if you have had high pressures due to a faulty expansion vessel
you might now have a leak in the pipework.

 

[Fluffster]

I think you are getting confused with the boiler sealed system pressure and the hot water pressure in your cylinder as they are 2 seperate things.

What expansion vessell was changed, the boiler or the cylinder?

If you mean the pressure guage on the boiler is dropping to zero then this has nothing to do with the tundish which relates to the stored hot water. The condensate again has nothing to do with the system pressure too (unless you have an internal leal in your heat exchanger)

Check for leaks throughout the system as it does not take much water to drop 1 bar. Check the prv put a bag on the warning pipe and see if it is letting by.

Make sure you are checking your system expansion vessell, usually red when the system has been drained.

Pete

 

[Syd98]

I've checked everywhere for leaks, no visible sign, no weapy valves. Anyway it could leak through the boiler heat exchanger?

 

[Syd98]

I understand the way the system works.. It's the system external exp vessel that was changed, I have tissue paper on the tun dish, so I know no water as passed throu, no leaks, my thinking was that the heat exchanger was leaking system water into the condensate drain... Is this possible or would Problem with the heat exchanger show else where..
One other question. If the external exp vessel was leaking air from the top up valve could each pressurization deflate the air side and that's where the pressure loss is , in the exp vessel,,?

 

[dcawkwell]

I understand the way the system works.. It's the system external exp vessel that was changed, I have tissue paper on the tun dish, so I know no water as passed throu, no leaks, my thinking was that the heat exchanger was leaking system water into the condensate drain... Is this possible or would Problem with the heat exchanger show else where..
One other question. If the external exp vessel was leaking air from the top up valve could each pressurization deflate the air side and that's where the pressure loss is , in the exp vessel,,?

with boiler and heating cold. Pressurise the system up to 2 bar.
Close the valves of the flow and return under the boiler.
Switch boiler off and wait a day. if pressure drops the heat exchanger in the boiler is leaking or there is a leak in the boiler somewhere.

 

[GavThePlumber]

When did you last replenishing the air gap?

 

[Syd98]

do you mean the air gap in the megaflo? it was done a while back but I was told only do this if water is dripping from the prv into the tundish? I thought the air gap is just to pressurize the hot water?

 

[GavThePlumber]

Right, so isolate the boiler.

 

[Syd98]

Latest findings... Expansion vessel ok.. No water down tun dish well at least not enough to dissolve 1 piece of Andrex, ch and HW on tonite for 3 hrs... Pressure gone.. And 1 litre of wAter out of boiler condensate.. Any sensible opinions.. No water leaks on rad valves or anywhere... Question.. Could my Worcester Bosch boiler be kaput.. Cuz this is all it he symptoms of the old boiler being kaput..

 

[twgas]

You cant check the heat exchanger the way you are trying to, use a bucket under the condense pipe but the boiler must be OFF so that any water in the bucket is system water, if boiler is on the bucket will have condense in so you wouldnt know if system water is with it or not.
I would be checking the connection between vessel and system, if the vessel is definitely ok.

 

[Syd98]

Had an engineer in yesterday, who fitted a new expansion vessel and said that should do the trick..,!
Woke this morning to clanking and pressure down to zero.. Rung the guy back who said your boilers prob had it.. Worcester Bosch 18i only 2.5 years old..
Just topped up ran a CH cycle. Pressure went from 1 bar to 2 bar, then as system cooled finally down to 0.25bar.
Retopped up and system bled, no running just HW see what happens, pressure 1 bar rises to 1.5bar, see what this drops back too as it cools back down?
How can I prove what the fault is without keep throwing good money after bad..

 

[Syd98]

Latest..!
Pressure drop is only when we run the CH.
HW pressure goes from 1 to 1.5 bar then back to 1bar.
CH goes from 1 to 2 bar then as cools pressure drops to less than 0.5bar.
The system is protected by a 3 bar blow off valve rwc cartridge type. Is it possible that this is letting slightly at about 2 bar? How reliable are they, or should they be replaced once they blow off?
Or.. Have we got a leak... But if so where's the water gone? No sign anywhere or have I hot to get all the floor boards up?
Is the sentinel leak sealer worth a shot or a complete no no?