Boiler rapidly losing pressure

Belenus

17 year old 4 bed standard construction 2 storey detached house with 17 year old Potterton Powermax HE 150 boiler; 13 steel radiators with small bore plastic pipework.

Working pressure for the primary circuit is 0.9 - 2.5 bar although I cannot get it higher than 2.1 via the filling loop.

We bought the house in 2011 and for most of that time we have only had to top up the system pressure every four months or so.

Recently it has started losing pressure more rapidly, dropping every couple of weeks and, in the last few days, it is now dropping from 2.1 bar to 1.0 bar in a few hours. It is also losing pressure when the CH and HW are both switched off.

It still operates as normal when required on CH and HW.

I have checked all the radiators and visible pipework for leaks and can find nothing. Perhaps the leak is in the boiler itself.

There is no evidence of the pressure relief valve actuating.

What is the correct sequence of checks and/or actions that I can do myself before calling in an engineer.

Is it worth trying a leak sealer such as Fernox F4?

Advice and suggestions welcome.

Thanks

bris

Hmm missed the bit about the prv, that is what I was going to sugest., tie a plastivc bag to it and see if it fills.

It could be a leak under a floor on the bottom level.

Is there a tank? Check the tundish.

FaceHead

Can you lock off the CH pipes where they exit the boiler? Then top up the boiler and see if it holds the pressure overnight?

This would tell you if it's the boiler or (most likely) a leak out under a floorboard somewhere. 

Another_Level

Well like everything its a process or elimination, visible water leaks & prv done and ok  great.

After re pressurising do you need to regularly bleed air from any radiators ?

That boiler has an integral expansion vessel on a flexi pipe, is it the original expansion vessel and has it been serviced during the last service visit ?
Also the heat exchanger could be pin holed and losing water down the condense trap-rare but possible.

Checking the air pre charge in the expansion vessel is essential before considering looking under floors up  or using leak sealer products 

There an ok gas boiler 

Belenus

bris said:

Hmm missed the bit about the prv, that is what I was going to sugest., tie a plastivc bag to it and see if it fills.

It could be a leak under a floor on the bottom level.

Is there a tank? Check the tundish.

Thanks for responding.

The Tundish is dry and the discharge pipe outside the house is dry. I have a container there to check.

It is a sealed system with no cold water storage tank. Everything is mains water only.

The only tank is the integrated 150 litre hot water tank.

Belenus

FaceHead said:

Can you lock off the CH pipes where they exit the boiler? Then top up the boiler and see if it holds the pressure overnight?

This would tell you if it's the boiler or (most likely) a leak out under a floorboard somewhere. 

Unfortunately not but thanks for the suggestion.

Belenus

Another_Level said:

Well like everything its a process or elimination, visible water leaks & prv done and ok  great.

After re pressurising do you need to regularly bleed air from any radiators ?

That boiler has an integral expansion vessel on a flexi pipe, is it the original expansion vessel and has it been serviced during the last service visit ?
Also the heat exchanger could be pin holed and losing water down the condense trap-rare but possible.

Checking the air pre charge in the expansion vessel is essential before considering looking under floors up  or using leak sealer products 

There an ok gas boiler 

I haven't checked that. I will tomorrow.

I presume that the expansion vessel is original. The boiler was last repaired/serviced about three years ago by Baxi who own Potterton. I, rightly or wrongly, don't have it serviced regularly. Maybe I should.

I have no idea how to check the pre charge etc so I will leave that to the professionals.

I have replaced the 3 way valve actuator so I know how to open up the boiler casing. I plan to open it up tomorrow to see if there is any visible leak inside the top section where all the action takes place. Three years ago the integral pump was leaking and it was replaced. You could see all the limescale debris from the leaking water. That leak had probably been there for months if not years as the small amount of leaking water evaporated in the hot environment before visibly leaking to the outside.

If you are not familiar with this boiler, it is an integrated unit with the burner, heat exchanger, pump, diverter valve etc all contained in a small space above an integrated 150 litre hot water tank. Everything is contained inside a large metal casing. I will post some pictures below.

Belenus

Some pictures.

The boiler casing. The top section above and behind the control panel contains the boiler etc. The bottom sections contain the 150 litre hot water tank. You can see the bottom part of the white expansion vessel top left.



The HW tank and pipework in the lower sections with the panels removed.



What I think is the mains cold water inlet pressure control. Am I wrong.

Ectophile

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.

Bendy_House

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.

The issue my sis had was that the pressure would increase too far when the boiler came on, and finally topped 3bar which opened the PRV. The resulting water/pressure loss then had to be made up again, and the cycle repeated. What often also happens is that the PRV simply doesn't shut off properly afterwards, so there's always a steady loss, but you have discounted this by checking the end of the 15mm copper pipe outside? That's a shame, as it's a relatively easy repair.

To repressurise the EV (the correct one...) first requires the system pressure to be lowered to zero, best done by bleeding a top-floor rad. Then, as the EV is pumped up (can't recall - over 1bar-ish?), more water will be expelled from the bled rad, which is important as the system pressure should remain at zero during this process. Once recharged, the bleed screw is shut, and the system repressurised (there's a valve there for this) to around 1bar (or somewhere above this for this boiler).

A peculiarity of this boiler is that the pressure fluctuates a lot in use. Even after recharging the EV, what would happen is that the instant the boiler - and pump - fired up, the indicated pressure would drop by around 0.3 bar. I suspect this is because the pressure sensor is on the 'return' side of the pump, and this would suffer a drop whenever the pump was running. This then meant that if the static pressure was slightly less than 1 bar, it could easily drop to 0.6 when the boiler fired up, and it would then go into lockout as the pressure was 'too low'... Bludy annoying. This was exacerbated by the system pressure then climbing a large amount - to well over 2 bar - whenever the boiler heated up fully, so was getting into almost 'too high' territory. Setting the static pressure was therefore a balance between high enough not to cause lockout, and not so high that it reached near 3bar when hot. A right b***er.

I was really concerned by how much the pressure would climb in this boiler - a very unusual range - until I read the instructions and found that anything up to 2.5bar (or so) could be considered 'normal'! Weird boiler, man.

Anyhoo, I digress - and rant. If there is no obvious source of a leak - ie nothing showing in the tundish (try leaving a piece of tissue paper across it - then it's sadly not the PRV (an easy replacement).

That basically leaves

(a) a leak in your pipework. Do you know if it's 10mm microbore pipe, run down behind your walls? If so, I'd suggest that any leak from this is both unlikely, and would also be very obvious.

(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.

(c) the only other leak source I can think of is the heating coil in the hot cylinder, again a possible pinhole. Having said that, it is both simply unlikely (very rare) in any case, but also the pressure of water in that cylinder will almost always be greater than that in your 'system', so - if anything - water would be flowing the other way! I think that can therefore be discounted.

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?

BUFF

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