Combi boiler slow leak advice

[Simba_ali]

Hello, 

 

I have a potterton promax combi boiler which has a slow loss of pressure, as an example I filled up to 1.3 bar and it's dropped to 0.9 bar in 2 months. 

 

I've checked all rads and visible pipework and tested the overflow pipe outside and no signs of water. Also there is no sign of staining on the ceilings from leaking pipework. 

 

The return valve on the boiler had a leak which I thought was the problem but that's been tighten and no more water is leaking from it. Also during the summer when the heating wasn't being used the boiler didn't seem to lose pressure or if it did it was a minimal amount and didn't need repressurising in 5 months until the heating was used again. 

 

Anything I can do without pulling all the floors up looking for a tiny leak??

 

Cheers 

[JFDIY]

Expansion vessel?

 

My sister's was ok in summer when the heating wasn't really used (she's super tight and thinks a 14⁰ house is acceptable.

 

Come winter it would need topping up every couple of weeks. The tell tale was when cold, the system pressure was about 0.75 bar but used to go to about 2 bar maybe more when running the heating. I witnessed it spilling water from overflow on one occasion. A new relief valve and expansion vessel and I haven't been called back.

 

 

 

 

 

[MikeGrahamT21]

How old are the rads? Older radiators will be corroding and letting off gas, most boilers have an air release valve built into them meaning pressure will drop over time. If thats the case, you probably need rads cleaning out and then fresh inhibitor adding to the system.

[Simba_ali]

Thanks for the reply 

 

Here is where it gets abit complicated.. 

 

If the pressure gauge is sitting at 1 bar cold  and I turn the heating on it will drop to 0.5 bar straight away temporarily and over about 20 minutes rise back up to 1 bar the same as the cold reading. When I turn off the heating the pressure reading rises to about 1.6 -1.7 but doesn't go above that. 

 

Does the fact the pressure doesn't drop with the heating off mean it's more likely to be a boiler problem? 

[Simba_ali]

  On 04/02/2021 at 11:53, MikeGrahamT21 said:

How old are the rads? Older radiators will be corroding and letting off gas, most boilers have an air release valve built into them meaning pressure will drop over time. If thats the case, you probably need rads cleaning out and then fresh inhibitor adding to the system.

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The boiler / radiators are only 4 years old so I hope this isn't the problem. At my last service they checked the inhibitor levels and they were fine. 

[MikeGrahamT21]

Dodgy pressure guage? Does tapping it move it?

[Simba_ali]

No tapping it doesn't move it. An engineer told me it was installed in the wrong place but the cold reading is the true pressure level 

[MikeGrahamT21]

In the wrong place? Usually they are part of the boiler.

 

Certainly can't rule out a leak under the floor if everything else checks out

[Simba_ali]

I have no idea lol, they were probably having me on...

 

How much water are we talking for a drop from 1.3 to 0.5 from 6 radiators in 3-4 months? How would I find that under the floors? Sounds messy...

 

[MikeGrahamT21]

Hard to know for sure, but you'll know roughly how long the taps are open when refilling, it won't be an insignificant amount I know that.

 

What type of pipe are you using to connect all the rads?

[Simba_ali]

It looks like flexible rubber type pipes? 

[MikeGrahamT21]

Probably PEX. If its continuous lengths between radiators shouldn't be any leaks, but if there are joints it could be one of those leaking.

 

PEX is meant to have an oxygen barrier to prevent air getting into the system, but even the best PEX this tends to only work to 50C maxmium, so there could be a bit of air ingress if its not up to spec, but still don't think it would add up to the amount your topping up. If you can view anywhere under the floor without destruction, see if you can see any joints in the pipe, if you can, then they will need inspecting until you find the rogue one.

[Simba_ali]

I'll have a look to see if any pipework can be seen. how would you explain the pressure not dropping during summer when heating not being used?

[MikeGrahamT21]

Sometimes leaks require a certain amount of pressure to leak if you know what I mean. Once it’s hot and pressure has risen that may be just enough to tip it over

Edited February 4, 2021 by MikeGrahamT21

[Temp]

  On 04/02/2021 at 12:30, Simba_ali said:

how would you explain the pressure not dropping during summer when heating not being used?

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Metal expands when hot.  

[Conor]

We had a similar drop in our system, a bottle of Fernox F4 fixed it. (in fact I think the rate of loss was a bit more than yours). Suspected a small leak somewhere hidden in the floor.

[Simba_ali]

  On 04/02/2021 at 14:29, Conor said:

We had a similar drop in our system, a bottle of Fernox F4 fixed it. (in fact I think the rate of loss was a bit more than yours). Suspected a small leak somewhere hidden in the floor.

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How does this stuff work? 

[Conor]

  On 04/02/2021 at 21:19, Simba_ali said:

 

How does this stuff work? 

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No idea. It blocks small leaks. I like to think it works like the movie Inner Space,  where there a crew of people in a microscopic submarine floating around and patching holes.

[TonyT]

Leak Sealer F4 is a internal leak sealer developed for use throughout a central heating system to seal small, inaccessible leaks and weeps which may cause pressure loss and boiler breakdown. Once dispersed within the system, the product finds the area of oxygen ingress and forms a polymer to seal the pinhole

 

quote from the manufacturer

[dpmiller]

Like an egg.

[Simba_ali]

Hey, 

 

Been doing some investigating...

 

The sealed system is split via 2 diverter units so upstairs and downstairs are controlled seperately from each other. 

 

I'm assuming the pressure gauge when cold is showing the overall pressure? If i turn both up and down heating on it rises from 0.9 to 1.6 in about 10 mins 

 

Is this an acceptable rise in pressure? Or does it offer any clues? I have a feeling the pressure is dropping when both sets of Heating are on at the same time.. Still no sign of water from the prv though. 

Edited February 15, 2021 by Simba_ali

[Temp]

I think those pressures are in the right range. The increase might be slightly larger than normal but not by much. Can't say its definitely a problem. 

 

Normal is around 1-1.5

An increase of more than say 1 suggests there might be an issue with the expansion vessel.

Anything over 2.5  is getting close to opening the PRV. 

[Simba_ali]

So I can pretty much rule out a problem with the expansion vessel? 

 

I definitely can't see any signs of leaks on the plastic pipework so it's either the heat exchanger or a leak in the wall but showing no signs...

 

 

[Temp]

  On 15/02/2021 at 14:48, Simba_ali said:

So I can pretty much rule out a problem with the expansion vessel? 

 

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I'd say yes. Normally they fail by filling with water instead of air then when the heating is turned on the pressure rises pushing water out of the PRV. The pressure rise appears within limits and no water coming out of PRV.

 

 

Edited February 15, 2021 by Temp

[Simba_ali]

  On 15/02/2021 at 15:26, Temp said:

 

I'd say yes. Normally they fail by filling with water instead of air then when the heating is turned on the pressure rises pushing water out of the PRV. The pressure rise appears within limits and no water coming out of PRV.

 

 

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Ah ok thanks for that, 

 

I also had an error about a month ago which was e168 "Printed circuit board lockout" and I just reset the boiler and it never happened again....didn't think much of it until now where I was thinking if a leaking heat exchanger could cause such an error? Maybe water on a circuit board or?