Central heating pressure loss

And before that, how often?

Was there any DIY or other work happening in the house? If so, check for screws which might have penetrated a hidden pipe, e.g. into floors/walls.

Any work near any of the plastic pipe, check that the pipe has not got strained where it goes into push-fit couplers - they can easily leak if the pipe isn't going into the joint straight. (Pipes should also be fully supported so they aren't pulling on any of the joints, but people who install push-fit rarely do this, as a strained joint will normally still last for a while after the installer has gone, and only wreak havoc later on.)

If the pressure goes up very high when the heating system first heats up after refilling, then the pressure vessel has likely failed, causing water to be ejected from the pressure relief valve to the outside, and then the pressure will rapidly drop when the system cools. Check the outside pressure relief outlet - a plastic bag held over the outlet with an elastic band will catch some water as evidence if this is happening.

snipped-for-privacy@newsguy.com used his keyboard to write :

If it were to come to it, you can drain the system and just fill it with pressurised air, to make it easier to find the leak. Air will leak out easier than water, but won't make a mess.

If the expansion vessel has failed, the water will have nowhere to expand as the heating comes on, hence it will blow it out via the safety valve. Fit a balloon over the end of the valve pipe, if that gets blown off or filled with water, you have found the cause.

For pipes in voids you might find an endoscope useful to avoid ripping up floors and ceilings e.g.

It is probably a fun toy as well :-)

pressuring twice.

Thank you for your replies.

There has been no diy work near the pipes.

After more investigation I can report the pressure rises a lot when the hea ting comes on and a copper pipe that sticks out of the external wall behind the boiler drips. Going by posts in this thread I assume that the expansio n vessel has failed. Is there any point testing the valve on the vessel for air pressure?

Is the answer replacement of the vessel? Is that a diy job?

I can not find the manual either the printed copy or online but I have take n the cover off and found the info sticker. It is a ikon 23t.

Correct.

Whether replacing the existing vessel is a DIY job or not will depend on the boiler (and your plumbing skills). However you don't necessarily need to replace the existing vessel. You could just leave it where it is and add another vessel at a convenient place. That should definitely be DIY-able.

- Cut pipe.

- Insert tee-piece.

- Plumb in expansion vessel - pipe - isolation valve - pipe - tee-piece.

The isolation valve is so that the next time you need to replace the expansion vessel, it will be a piece of piss. You don't need a full bore isolation valve or anything - there will be hardly any flow through it.

Um, yes. If water comes out, the diaphram has split and the vessel is dead. If no water comes out, the vessel might just need pumping up with a bicycle pump (and implies the tyre valve itself may be leaking).

If it needs pumping up, it might say what the pressure should be on it (this is with the heating system depressurised). ISTR that mine says 0.75 bar (about 11 lb/sq inch on a tyre pressure guage).

It should be connected in the pipework near the pump inlet, to maintain constant pressure at the pump inlet which reduces cavitation in the pump (which otherwise causes noise and wear on the impeller).

I would certainly try pumping up the bladder inside the vessel. ISTR my last such system had to be 12 psi, or was it 2 psi best check online :-)

Mike

As others have intimated, you need to find out whether it really *has* failed, or has just lost its charge pressure.

Do the following:

1. De-pressurise the wet system (if necessary) by bleeding some water out until the pressure gauge reads zero
2. Check the pressure at the air valve on the expansion vessel with a car tyre pressure gauge. [If water comes out of the valve, the vessel is definitely shot, and will need to be replaced or an additional one fitted].
3. If no water comes out but there is little or no pressure, use a car foot pump (operated by hand) to blow it up to about 0.7 bar (10psi). Re-fit an air-tight cap to the valve just in case the valve itself leaks.
4. Re-pressurise the wet system to 1 bar, using the filling loop
5. Run the system and see what happens

If all is well after a couple of days, you've fixed it. If it's still losing pressure, further investigations will be needed.

Let us know how you get on!

So far so lucky. There was no water at the valve so I pumped the vessel up and repressurised the water. So far it has been running okay.

I guess with all the water in and out the system it would benefit from more rust inhibitor? Is it possible it add too much?

Was the air pressure in the vessel low? To what pressure did you pump it up? Did you do it with no pressure on the water side?

It's probably better to have too much inhibitor rather than too little. I'm not aware of any adverse consequences of over-dosing - but others may know differently!

I drained some water from the system so the gauge on the boiler read zero before I inflated the vessel. The air pressure gauge I was using started at 5 psi, so all I can say was the air pressure was less than that. I inflated it to about eleven psi.

Good. Sounds about right.

Thanks for your help.