Losing pressure in Central Heating system - going crazy!

cheme7676

ThisIsWeird said:

A thought, tho', Cheme. When you isolated the F&R CH pipes from the boiler, did you keep on using it to deliver DHW?
If not, worth doing. Monitor the boiler during a good 5-minute shower. Note starting, running, and end pressures. 

I haven’t, I tried to initially but when I turned hot water on with boiler isolated, the pressure continued to indefinitely increase nearing 2.5 bar. So i stopped because I didnt want to life the PRV as I was worried about it not reseating and then would have 2 issues to deal with. Just to confirm is this to test if the secondary heat exchanger is the faulty one?

ThisIsWeird

cheme7676 said:

ThisIsWeird said:

A thought, tho', Cheme. When you isolated the F&R CH pipes from the boiler, did you keep on using it to deliver DHW?
If not, worth doing. Monitor the boiler during a good 5-minute shower. Note starting, running, and end pressures. 

I haven’t, I tried to initially but when I turned hot water on with boiler isolated, the pressure continued to indefinitely increase nearing 2.5 bar. So i stopped because I didnt want to life the PRV as I was worried about it not reseating and then would have 2 issues to deal with. Just to confirm is this to test if the secondary heat exchanger is the faulty one?

It's to test the MainX. If it has a crack that only opens up with temp, then your isolating test would need to have it running.

The boiler shouldn't have that pressure issue - it doesn't rely on the radiators to provide extra expansion. The built-in EV should take care of this.

Yes, if the EV isn't doing its full job, then the rads and pipes will 'help' in normal use - ie they will 'bulge' fractionally to accommodate the expanded water, so it shares the load with the EV. But the rads shouldn't be needed. So possibly your EV isn't charged up correctly - 'ok' but not 'ideal'.

I don't blame you for not wanting the PRV to blow...

If you fancy trying it again, just keep monitoring the pressure, and stop if it goes above 2.5. It should be able to get comfortably close to 3 before any PRV opening. You could even lower the starting pressure to below 1, whatever your boiler can cope with whilst still firing up.

I'd personally want to do this test, tho'. From what you describe, the pressure loss only occurs (or mainly does) when your system is hot, and no real loss when cold. So, it needs to be 'hot'!

If you lower the starting pressure, then obviously note that down, and then see whether the end pressure, when cool, is different.

cheme7676

ThisIsWeird said:

cheme7676 said:

ThisIsWeird said:

A thought, tho', Cheme. When you isolated the F&R CH pipes from the boiler, did you keep on using it to deliver DHW?
If not, worth doing. Monitor the boiler during a good 5-minute shower. Note starting, running, and end pressures. 

I haven’t, I tried to initially but when I turned hot water on with boiler isolated, the pressure continued to indefinitely increase nearing 2.5 bar. So i stopped because I didnt want to life the PRV as I was worried about it not reseating and then would have 2 issues to deal with. Just to confirm is this to test if the secondary heat exchanger is the faulty one?

It's to test the MainX. If it has a crack that only opens up with temp, then your isolating test would need to have it running.

The boiler shouldn't have that pressure issue - it doesn't rely on the radiators to provide extra expansion. The built-in EV should take care of this.

Yes, if the EV isn't doing its full job, then the rads and pipes will 'help' in normal use - ie they will 'bulge' fractionally to accommodate the expanded water, so it shares the load with the EV. But the rads shouldn't be needed. So possibly your EV isn't charged up correctly - 'ok' but not 'ideal'.

I don't blame you for not wanting the PRV to blow...

If you fancy trying it again, just keep monitoring the pressure, and stop if it goes above 2.5. It should be able to get comfortably close to 3 before any PRV opening. You could even lower the starting pressure to below 1, whatever your boiler can cope with whilst still firing up.

I'd personally want to do this test, tho'. From what you describe, the pressure loss only occurs (or mainly does) when your system is hot, and no real loss when cold. So, it needs to be 'hot'!

If you lower the starting pressure, then obviously note that down, and then see whether the end pressure, when cool, is different.

Good idea actually, something I can definitely try this weekend.

This is where my knowledge of CH systems comes to a stop though, so just want to ask something out of clarity. Please correct me if I’m wrong anywhere.

1. We want to isolate the boiler and only activate DHW
2. DHW only runs through the secondary HX where it’s heated by the gas

If I understand that correctly then a couple of things I’m thinking of here:

1. If our suspicion is the primary HX leaking only when hot, but only the secondary is getting hot. How does this help me close in on the issue?
2. Assuming it doesn’t drop in pressure, then I still wouldn’t know if the primary HX is leaking because it’s not getting hot enough to leak (or is it?)

Of course it all depends on whether or not the primary HX does get hot (enough) when running DHW, which I don’t know the answer to. If we can confirm that running the DHW does increase the temperature of the primary HX significantly, then when I do the test, any pressure loss would signify issues in the primary HX. If no pressure loss is observed, then it points to the system. Does that sound about right?


I apologise in advance if I’ve got my wires twisted.

ThisIsWeird

The 'MainX' is the only one that's heated by the gas burner. The heated system water in the MX is then diverted - by the diverter valve - either around your radiators, or - if a hot tap is opened - around the 'secondary' or PlateToPlate exchanger.
When a hot tap is opened, a flow switch detects this and diverts - circulates - the heated MX water around the P2P exchanger, where it exchanges this heat with the cold mains passing through, to become hot water. So, the MainX is being tested, but needs to be run for a few minutes to ensure it's fully heated up, exposing any possible crack in it.

cheme7676

ThisIsWeird said:

The 'MainX' is the only one that's heated by the gas burner. The heated system water in the MX is then diverted - by the diverter valve - either around your radiators, or - if a hot tap is opened - around the 'secondary' or PlateToPlate exchanger.
When a hot tap is opened, a flow switch detects this and diverts - circulates - the heated MX water around the P2P exchanger, where it exchanges this heat with the cold mains passing through, to become hot water. So, the MainX is being tested, but needs to be run for a few minutes to ensure it's fully heated up, exposing any possible crack in it.

Got ya, makes perfect sense and actually a good way to confirm whether or not the boiler is at fault or not. 

So basically if it does leak, then bam it’s the HX. If it doesn’t then it confirms that it’s probably a system leak. Just to be 1000% sure, il still do this with the perfume trick and analyse the smell of the condensate, that should be enough evidence for me to change out the boiler.

Having said this, it does give me another question if like your advice on. Ideal offer a £345 one-off repair for all boilers under 15 years old (which mine is). Given that I’ve already changed a lot of parts and that the HX is the most expensive, do you think it’s more worthwhile going down that route to get use of it for a few more years? The boiler works excellently in all fairness and is very responsive, I’m just struggling with this pressure loss.

ThisIsWeird

I suspect you'll find that the MainX ain't covered   Or, they'll just say there's too many other bits on the verge of going wrong, so BER.

I would usually suggest to keep boilers going for as long as you can, but it obviously does come down to just what the fault is.

If the isolated boiler loses pressure, it'll be via the safety pipe or the condensate one - the latter if it's a cracked MainX. Your cond pipe is tricky to monitor - and some condensate will be coming out anyway - but it's worth putting a wee bag over the safety pipe just to cover all bases.

cheme7676

ThisIsWeird said:

I suspect you'll find that the MainX ain't covered   Or, they'll just say there's too many other bits on the verge of going wrong, so BER.

I would usually suggest to keep boilers going for as long as you can, but it obviously does come down to just what the fault is.

If the isolated boiler loses pressure, it'll be via the safety pipe or the condensate one - the latter if it's a cracked MainX. Your cond pipe is tricky to monitor - and some condensate will be coming out anyway - but it's worth putting a wee bag over the safety pipe just to cover all bases.

Thanks, sounds like a plan to me. So my plan of action this weekend:

1. Put some smell tracer into CH circuit, let it run for a short period for the substance to mix in
2. isolate boiler and maintain DHW
3. Keep bag tied around PRV outlet
4. monitor pressure loss and water from condensate
5. If pressure lost and condensate water (should) smell, boiler will need repair/replacement
6. if no pressure drop and no smell, deisolate and run CH system to try and track the smell in the house to see if I can track down leak to a valve

i think that sounds pretty solid to me. Now it’s just about deciding what smell to use. You quite rightly said something distinct but I also want it to be something pleasant because if it’s a leak in someone’s bedroom, they aint gonna be happy with that constant smell!

debbie2311

Having an identical experience. Same boiler make and model,  also house built in 2012. Thanks for posting this as I am at a loss, and going to read through replies now. If you find anything please post with an update- I will do the same. 

cheme7676

debbie2311 said:

Having an identical experience. Same boiler make and model,  also house built in 2012. Thanks for posting this as I am at a loss, and going to read through replies now. If you find anything please post with an update- I will do the same. 

Sorry to hear you’re struggling too!

you may not have realised but the fact we have identical boilers installed at similar times does indeed point to the boiler itself. It could be that the heat exchangers don’t last well beyond 12 years on this type.

in any case we crack on with the investigation and keep each other posted on here. The more evidence we gather that the boiler is faulty, the better. The last thing we would want to do is replace a boiler with a shiny new one and still experience a pressure drop. The constant fresh water would start rusting the whole system.

Have you already done the same tests that I mentioned in my first post by the way?

ThisIsWeird

cheme7676 said:

i think that sounds pretty solid to me. Now it’s just about deciding what smell to use. You quite rightly said something distinct but I also want it to be something pleasant because if it’s a leak in someone’s bedroom, they aint gonna be happy with that constant smell!

And monitor the pressure carefully as you reopen the isolating valve.

There are lots of these wee bottles of concentrated smelly oils - peppermint, lemongrass, lavender, pine, orange, eucalyptus... Which one would be the most noticeable to you - the least like current ambient smells?