Boiler rapidly losing pressure

Belenus

Ectophile said:

Normally, you'd pressurise to the lower end of the "normal" range while the system is cold.  As the radiators warm up, the water will expand and the pressure will rise.  If this exceeds the maximum pressure (usually about 3 bar), then the pressure relief valve vents.

Have you checked the pressure while the boiler is running?  If it goes outside the "normal" range, then either you've over-pressurised it, or the expansion vessel has failed.

The pressure drops as soon as the boiler and pump start. I have never observed the pressure rising above 2.1 bar which is the maximum I can reach via the filling loop.

The is a pressure limiting valve on the incoming mains just after the stopcock that is set to 3.0 bar so I am unsure why I can only get 2.1 bar maximum in the CH system.

Perhaps the inlet control group limits the pressure to 2.1 bar. I will read up on that device.

Edit: From the manual.

A multi-function Inlet Control Group is supplied with every Powermax HE. To ensure safe and splash free operation, mains water must be supplied to the boiler via the Inlet Control Group as indicated in Fig. 11 on Page 18.

Inlet Control Group (set pressure 2.5 bar)

Belenus

Bendy_House said:

Hi Belenus.

I am slightly familiar with these as sis-in-law has one in her house, and it had pressure issues.

There is a large, red, barrel-shaped EV above the boiler? I think (that's 'think' only) that is for the pressurised hot cylinder (DHW) and not for the actual boiler system.

I 'think' that the system's EV is actually behind that top panel - it's a flat-shaped vessel, with the typical Schrader 'tyre' valve on it.

Yes, there is a Primary Expansion Vessel inside the boiler casing and a barrel shaped Secondary Expansion Vessel (white rather than red) outside and above the casing. 

Belenus

Bendy_House said:

(b) a leak from the main exchanger - a pinhole as A_L says - which would have the system water trickling out the condensate pipe, so hard to detect amongst the usual condensate discharge. However, if your system is losing a noticeable amount of water even when the boiler is off, then that would mean a trickle from this plastic pipe when it shouldn't. So, is the end of the condensate pipe obvious outside your house? If so, wait a good half-hour after the boiler is last used, place a container under the cond pipe end, repressurise the system to, ooh, 1.5 or so (note it down), and leave the boiler unused for as long as possible - a day or overnight. Then check the pressure and the contents of the container.

The condensate connects to the house drainage somewhere under the floorboards so I cannot check that.

What I can do is get a bucket ready and remove the grey flexible condensate pipe from the white rigid pipe, (see the pipework picture above on page 1) and do what you suggest.

Thanks.

Bendy_House

BUFF said:

Bendy_House said:

On a different note, I'm guessing the reason you cannot get the system pressure above 2.1bar (and thank the lawd you cannot...) is because your mains pressure is at this level. I don't know what that object is in your last pic - could you post a closer pic of the label?

A quick Google suggests "potterton powermax 5106013 inlet control group" e.g. https://www.cityplumbing.co.uk/Potterton-Powermax-5106293-Inlet-Control-Group/p/491820

https://picclick.co.uk/POTTERTON-POWERMAX-5106013 Inlet-Control-Group-c-w-Tundish-and-263786291409.html

Nice! That's the baby, BUFF.

Seemingly a PRV, so that the cold supply's pressure to the cylinder is controlled, and a cold take-off is also available to feed a shower so they are nicely balanced. Good chance this is what's limiting the boiler's supply pressure to just over 2.1bar.

Bendy_House

Belenus said:

Bendy_House said:

(b) a leak from the main exchanger - a pinhole as A_L says - which would have the system water trickling out the condensate pipe, so hard to detect amongst the usual condensate discharge. However, if your system is losing a noticeable amount of water even when the boiler is off, then that would mean a trickle from this plastic pipe when it shouldn't. So, is the end of the condensate pipe obvious outside your house? If so, wait a good half-hour after the boiler is last used, place a container under the cond pipe end, repressurise the system to, ooh, 1.5 or so (note it down), and leave the boiler unused for as long as possible - a day or overnight. Then check the pressure and the contents of the container.

The condensate connects to the house drainage somewhere under the floorboards so I cannot check that.

What I can do is get a bucket ready and remove the grey flexible condensate pipe from the white rigid pipe, (see the pipework picture above on page 1) and do what you suggest.

Thanks.

Cool - that's one to try.

You clearly have a good handle on what's involved. That 'inlet control' thingy might well be 'set' to 2.5bar, but is seemingly only providing a max of 2.1b. That could, of course also be due to your main PRV being a bit sticky and also limiting the forward pressure to 2.1 even tho' it's set to 3 bar. Or perhaps - ie not impossible - that you actual incoming mains isn't much above 2bar!

Does your 'main' PRV have a gauge on it? If so, does it remain pretty much at 3 bar even when a tap is run?

Anyhoo, you certainly don't want your 'cold' or starting pressure to be over 2 bar! From what you describe, yours does what sis's does - the pressure blips down whenever the boiler fires up. It would then typically slowly climb as the boiler heats up the system water. With most boilers, you wouldn't want this to be a dramatic climb, and I'd personally be concerned if it increased by more than 0.5bar, and wouldn't be happy with a pressure over 2bar at any point. However, these boilers are 'weird', and such pressure fluctuations are seemingly quite normal, and the instructions indicate a very wide acceptable pressure range.

Sis had problems when she topped it up to around 1.5bar - a reasonable (if slightly high for my liking) level. However, this meant it hit nearly 3 bar when fully hot, and this opened the safety valve = dumped system water = cold pressure then below operating figure. Plus, the safety valve kept on dripping. An EV recharge kept the pressure climb under some control (tho' I still hate the way it soars), along with a new safety valve (peasy) seemingly sorted it.

Keep us posted :-)

MeLindsey

We had a very similar problem with our boiler, the pressure drop started off slow then over the weeks got worse and worse until it was taking about 20 minutes to drop completely. The boiler always operated normally until the pressure went out of range.

It turned out to be a leak, where the water was going down an external wall and there was never any visible water damage.

We had a fairly new extension and new radiators/pipes in the older part of the house, we got our builder back, he checked the new radiators/pipes which seemed fine.
He isolated the pipes to the extension, the pressure stopped dropping and the boiler worked fine.
We left it a bit to be certain, then he opened up the wall in the extension to access the pipework.

Turns out a mouse had chewed through the pipe. We caught the mouse, our builder fixed the pipework.
All fine and no new boiler needed. 

Bendy_House

Eeeek! Or should I say, squeeeeek.

Belenus

An update as I don't like to see threads unresolved.

Since last posting I have done nothing but occasionally check on the pressure reading. It varies between 0.8 bar and 1.5 bar when the boiler is firing and settles at 1.1 to 1.2 bar when not firing. The display flashes when the boiler is firing and the reading is 0.9 bar or below.

The User Instructions state:

We recommend that the system pressure when cold be between 1.0 and 1.5 bar. If the pressure is falling the status display will flash P 0.9 or lower and it is advised to top up at this stage. If the pressure drops below 0.5 bar the boiler will not light.......

The boiler appears to be quite happy with lowish pressure so I plan to continue to do nothing until or unless the pressure drops further or the boiler locks out. I will then top up the pressure again which should result in the boiler firing up again. It will be no hardship to top up occasionally if that is all that is required to keep the boiler running. There should be enough Fernox remaining in the circulating water for that not to be a worry.

I will post again if anything changes.

Thanks for all your contributions.

Belenus

Another update.

I finally got around to removing the front panels from the boiler today and I can now see drops of water falling into the Tundish so it would appear that the Pressure Relief Valve (red in the photo) is leaking. It is leaking at about one drop every couple of seconds which is perhaps slow enough for the water to evaporate inside the discharge pipe before it exits at ground level outside the house and that may explain why I saw no evidence there.

That is probably good news as a new valve is only about £20 plus whatever I have to pay someone to install it.

A leak in the pipework somewhere under the floorboards would be far more expensive and disruptive to resolve.

I may wait until warmer weather to get it replaced just in case something goes wrong and we lose the heating entirely. Once the pressure drops to about 1 bar it seems to stop leaking and the boiler seems quite happy at that pressure.

Hopefully the problem is not with a faulty expansion vessel.

Bendy_House

That's good news, Bel. And, as you say, the part is cheap, and it's also easy to replace.

Provided the pressure doesn't go far over 2 bar, then the replacement PRV should be ok, but I suspect the plumber will want to check and recharge the EV while they are there - it's an obvious thing to do, and is also quick and easy (the water side will have been depressurised anyway, which is needed for this).

I doubt very much the EV is faulty - ie punctured - as the pressure soaring would, I think  be a LOT more than what you are seeing.

Annoyingly, when i swapped my sis's PRV and recharged the EV, the boiler still had pressure increases while hot which were far more than I was used to with 'normal' boilers, but I was relieved when the instructions said that the wide pressure range seen was 'normal'. On most boilers, you wouldn't want or expect the pressure to be getting anywhere close to 2 bar, but above this is 'fine' for this weird boiler

Your current pressures are absolutely fine.

That it flashes at 0.9 and below is fine too - that's just an early-warning device, and the boiler will be fine until it falls to the lower figure whereupon it'll stop working in any case.

Yes, always keep a system pressure as low as will perform the task - less stress all 'round.

When you do finally get it replaced, ask the cove to also add more inhib.