Boiler losing pressure, need help finding the cause (leak?)

ThisIsWeird

I understand a useful aspect of a 'combi' boiler is that it can be kept running for DHW with the radiator system fully isolated from it via the valves under the boiler. If the pressure continues to drop, the leak will be from within the boiler.

But - pressure check and discharge pipe check first.

diystarter7

ThisIsWeird said:

I understand a useful aspect of a 'combi' boiler is that it can be kept running for DHW with the radiator system fully isolated from it via the valves under the boiler. If the pressure continues to drop, the leak will be from within the boiler.

But - pressure check and discharge pipe check first.

Hi
What I was going to post

Check if there is any evidence of dried water/gunge under the boiler/pipes

However, I'm almost 100 cetain thei is a leak, pinhole type and the reason ti is not showing is it drys out with the heat.

So check and check the combi, exposed pipes etc and if still leaking, try a leak sealer and IMO that will fix it, at least massively reduce the loss of waters

NB: Once you have done that at the same time add more inhibitor as pin leaks are often a result of rust/gunge - but it could be a poor connection on new pipes somewhere

Good luck

ThisIsWeird

Yes, there could be a heat-affected leak. The pressure loss is pretty dramatic, tho', with sometimes a drop from 2bar to zero in a few days - that would usually represent a few cupfuls of water - and it doesn't happen when the CH is not being used.

Bullit_2600

locky123 said:

Checked the pressure relief valve isnt dripping from the discharge pipe?  Checked the expansion vessel is holding the correct pressure? Cracked heat exchanger?

How do I check the expansion vessel is holding the correct pressure?  Is that for a plumber to do or something I can?

ThisIsWeird

Bullit_2600 said:

locky123 said:

Checked the pressure relief valve isnt dripping from the discharge pipe?  Checked the expansion vessel is holding the correct pressure? Cracked heat exchanger?

How do I check the expansion vessel is holding the correct pressure?  Is that for a plumber to do or something I can?

Don't touch the EV. Please do this - locate the safety discharge pipe going outside your house from the boiler - it'll likely be on the nearest wall to the boiler. It'll be 15mm copper, and either point down close to the ground, or will bend back on itself and point against the wall. When you find it, tie or tape a small clear plastic bag over the end to monitor any discharge - there should be none.

locky123

Bullit_2600 said:

locky123 said:

Checked the pressure relief valve isnt dripping from the discharge pipe?  Checked the expansion vessel is holding the correct pressure? Cracked heat exchanger?

How do I check the expansion vessel is holding the correct pressure?  Is that for a plumber to do or something I can?

This should have been checked by a competent Gas Safe registered engineer in the last 2 years if you've had it serviced. I suggest you get a competent gas engineer to check/service your boiler, they can confirm whether the expansion vessel and pressure relief valve are both OK. I wouldnt advise a novice to other than check if the discharge pipe is dripping and monitor record the pressure gauge readings during operation. Your starting from a higher than normal cold pressure at 2bar, which means that the pressure is increasing when operating to perhaps near the typical pressure relief valve (PRV) release pressure at 3bar. The PRV once opened may not reseal 100% so could be dripping, resulting in the pressure loss. That is why you should check the discharge pipe which is connected to the PRV. As suggested look at the pressure gauge when cold and also during heating, this will indicate possible causes. Typical combi pressure at cold is 1bar, the gauge should show this range.

JohnB47

ThisIsWeird said:

Bullit_2600 said:

locky123 said:

Checked the pressure relief valve isnt dripping from the discharge pipe?  Checked the expansion vessel is holding the correct pressure? Cracked heat exchanger?

How do I check the expansion vessel is holding the correct pressure?  Is that for a plumber to do or something I can?

Don't touch the EV. Please do this - locate the safety discharge pipe going outside your house from the boiler - it'll likely be on the nearest wall to the boiler. It'll be 15mm copper, and either point down close to the ground, or will bend back on itself and point against the wall. When you find it, tie or tape a small clear plastic bag over the end to monitor any discharge - there should be none.

But the OP said that an external expansion vessel has been fitted, presumably to back up an existing internal one.

Isn't it highly unlikely that both vessels are at fault here and therefore that the pressure release valve is not being triggered or is dripping?

An easy thing to check though.

ThisIsWeird

JohnB47 said:

ThisIsWeird said:

Bullit_2600 said:

locky123 said:

Checked the pressure relief valve isnt dripping from the discharge pipe?  Checked the expansion vessel is holding the correct pressure? Cracked heat exchanger?

How do I check the expansion vessel is holding the correct pressure?  Is that for a plumber to do or something I can?

Don't touch the EV. Please do this - locate the safety discharge pipe going outside your house from the boiler - it'll likely be on the nearest wall to the boiler. It'll be 15mm copper, and either point down close to the ground, or will bend back on itself and point against the wall. When you find it, tie or tape a small clear plastic bag over the end to monitor any discharge - there should be none.

But the OP said that an external expansion vessel has been fitted, presumably to back up an existing internal one.

Isn't it highly unlikely that both vessels are at fault here and therefore that the pressure release valve is not being triggered or is dripping?

An easy thing to check though.

Fair enough - an external one should be easy to check. The results could largely be meaningless, tho', as the air side will be affected by the water side, regardless of how much - or how little - air is inside it. Unless water spurts out, of course :-)

If the 'system' is currently pressurised to 2bar, then the air side of the EV will also indicate this pressure, so a deceptive reading. Really, it needs the system side to first be depressurised, and then a reading taken of the air charge pressure.

I think.

The easy, layman, check is to see if owt is coming out t'pipe.

locky123

Expansion vessel pressure is checked when the system and/or boiler is depressurised.

Bullit_2600

Just responding to some previous comments, the reason we were topping up the pressure to 2 bar was on advice from the plumber to give us a few days where we didnt have to top it up and we've just kept doing it.

And during winter we are doing this once / twice a week.

In the summer we didnt need to do it so the problem only occurs when the central heating is on.

Unfortunately the pipes are boxed in but I cannot see any signs of leaks under the boiler which the same plumber has also checked for leaks and did not find any.

Doesnt mean that isnt the cause though maybe it was missed.

As mentioned boiler is only 2 years old so I'd hope it wasnt a cracked heat exchanger (which was previously checked) and also all radiators are new.  May mean there is a chance of error at installation?

I have just completed the following actions today:

1. Bleed radiators - DONE - all ok as had bled them last week so no air.

2. Check they are all tight - DONE

3. Tighten valves on radiators - DONE

4. Place paper tissue round each rad pipe - DONE

5. Tie clear bag around discharge pipe (comes straight out the wall by boiler) - DONE

6. Top up boiler to 1.2 - DONE (was at 2 so I had to bleed a radiator to get it down to 1.2 (2.5l of water)

7. Confirm what pressure gauge is after turning on

      (a) after 1 min   = 1.5

      (b) after 30 mins = 1.9

      (c) after 60 mins = 1.9 with dial flickering to 2

      (d) 10 mins off   = 1.5

      (e) 30 mins off   = 1.4

      (f) 60 mins       = 1.2

I'll keep an eye on the pressure gauge and the tissue paper for any signs of leaks.

Really appreciate all the comments and help