Combi Boiler Pressure Dropping - Re-Filling Most Days

[cwcw]

We have an Alpha boiler, around 9 years old. It's a combi boiler but not a condensing one.

It came with the house we bought and we noticed the pressure was dropping gradually. Every 10 days or so, I would just top it up with the filling loop and it would be ok. However the length of time has got shorter and shorter between filling. An engineer looked at it today but seemed to pose more questions than answers. Here are the symptoms:

- Pressure drops below minimum and so boiler fails to start up. This usually occurs after a long(ish) period of being unused, e.g. heating off when out all day, or overnight. The frequency of this has become more and more often.

- Pressure still goes up when heating is on. Engineer asked if it gets to the highest extreme, but it only ever seems to each 2 bar when on, sometimes a bit over.

- I did the bag test on the outside pipe. Due to weather and plastic bags having holes in, it's not conclusive but I think there is a slight drip.

- It does not seem to take much refilling to put the pressure back up to the usual 1.2ish bar to fire the boiler up. I would say I hold the valve for a few seconds.

- There are no obvious signs of leaks anywhere, other than the TRV on one of the radiators kept developing a small puddle after I turned it down once. I think I had accidentally loosened the connection to the pipe so I took it off and put it back and not noticed any leak from it again.

- The radiators have started to make a bit of a hissing noise when the heating is on. This has only recently started and probably due to the constant refills creating air bubbles I guess. I don't think this is a cause.


Any suggestions of what could be wrong or what else to look for to help pin point the problem?

The engineer thinks either a leak somewhere, which will be near impossible to find, or a new expansion vessel, which he thinks will be cost prohibitive and may as well get a new boiler, unless we do some kind of bypass (didn't really understand this).


Thanks.

 

[Exbg]

Can you access all your pipe work? I.e have you any under floors etc?

 

[cwcw]

All pipe work, apart from immediately under the boiler and either side of each radiator, is fully plumbed in under the floorboards.

Does it sound like a pipe work leak? To be honest I'd rather it be some £400 fault with the boiler than a £10 leak in a pipe that needs all carpets, floorboards, tiles and laminates to come up.

 

[Exbg]

Deffinatly sounds like that...can be pressure vessel but your pressure would usually go sky high when heated if it was tha

 

[onecog]

"I did the bag test on the outside pipe. Due to weather and plastic bags having holes in, it's not conclusive but I think there is a slight drip"


That is the first place i would be looking.

 

[MANDATE]

My view is that if the PRV is dripping slightly, it most likely has been opened at some time. This could be manually during a service or activated due to pressure reaching 3 bar.
It is common for these valves not to seat correctly on closing due to sediment on the seating face.
The PRV could be dismantled and cleaned but the easy way is just to replace it with a new one.
During replacement the 'air' charge in the vessel should be checked and adjusted if need be, otherwise any fault with the vessel or the connecting pipe (blockage) may activate the PRV and you could be back to square one with it dripping.
Air charge with zero water pressure needs to be about 0.8 bar then water pressure needs to brought up to the same or slightly over. say 1 bar.
With heating on pressure should rise about 1 bar.
It does sound that the vessel is OK but still worth checking out.
The replacement of the PRV seems to be the next obvious step

 

[Exbg]

Turn your heating on and leave it until it reaches full temp and see if you get any drips from blowoff

 

[cwcw]

Ok, I'm going to use a plastic bottle on the pipe outside to conclusively see if any water drips out.

On another note, I have found one of the radiators leaks quite heavily when one of the valves is turned. If I close the valve on it, water drips out quite noticeably. The valve is usually fully open and it's the only one without a proper TRV fitted. Could this be related? e.g. when fully open it could still be leaking a very small, unnoticeable amount over a prolonged period.

Also I have read you can isolate the pipework from the boiler. I can see the inflow and return for the heating pipes, and where they connect there is some sort of screw and connection, but I've no idea how to do it. It looks like you could turn the screw and it somehow acts as a valve. Is anyone familiar with these connections and how to disconnect?

 

[Whitespirit66]

If you have a leaking non-TRV valve, you could try removing the head/cover and tightening the nut underneath if this is where the water is coming from.

Then do the bottle on the blow-off pipe to see if PRV is leaking.

These 2 things will help to rule in or out whether you need to look elsewhere.

 

[cwcw]

This might be a daft question but how do I get the plastic turning valve off the pipe to be able to tighten the nut? It seems to only allow fully open or fully closed, can't work out how it comes off the thread.

 

[danplumb]

This might be a daft question but how do I get the plastic turning valve off the pipe to be able to tighten the nut? It seems to only allow fully open or fully closed, can't work out how it comes off the thread.

It just pulls off.

 

[onecog]

This might be a daft question but how do I get the plastic turning valve off the pipe to be able to tighten the nut? It seems to only allow fully open or fully closed, can't work out how it comes off the thread.

It just pulls off.

He might break it if he does that or lift the rad off the wall
There should be a ring just below the TRV plastic top ?......unscrew it

 

[cwcw]

It's not a TRV, they unscrew easily. It's a plastic cap.

 

[Whitespirit66]

One hand on the valve and pipework to steady it, other hand on cap and pull upwards.

 

[cwcw]

Ok, update... there is a small leak at a radiator valve, but probably the main leak is from the pipe that goes outside. This collected around 200ml in a day. What does this point to? Don't want to get ripped off.

Thanks