Dropping combi boiler pressure - finding the leak?

[lizziecupcakes]

Hi all, I wrote about this about a year ago:

We had a new ecotech vaillant combi boiler fitted in last year (the previous water tank one was going bust and we opted for a combi, which we prefer). Anyway, the old water tank one didn't have a pressure reading thing that we could follow before removing it (or maybe it did but we didn't see it!).

Since adding the new combi boiler we noted that the pressure drops very slowly over a few months, and in one year, we had to top it up twice. we had a vaillant engineer come round a few months ago (the actual plumber who did the work did a good job but was a complete a-h*le - sorry for the profanity! But he was and refused to help us). Anyways, the vaillant engineer did his work and looked at as much of the pipes to the radiators as he could, and he found one slight leaking point at the valve of one radiator, but he said it was quite tiny that he didn't think that was the actual cause of the leak because the drop in pressure we were/are still seeing doesn't suggest it's that. We still haven't fixed that leaky point but intend to by actually replacing that entire radiator and part of the pipes going into it (that radiator is too low BTU for the room).

It's been awhile now and I'm returning now in this thread to discuss ways to fix this leaking issue i'm not sure how to go about looking for this leak myself.

I am aware that I may never find it. We hope that in about 10 years (lol) we may have saved enough to do a reno and extend our downstairs kitchen, and that's when we could probably see about changing all the radiator pipework through the entire house. Maybe this would fix any future leak issues too and well have some peace of mind for a few decades from then.

But in the meantime, I have no idea what to do with our current pressure drops, and I'm concerned that it's damaging our new combi boiler.

The drop in pressure we are seeing is , for example, from 1.7 to 1.4 over about 4-5 months. I think that's a small drop?

One plumber did suggest we use sealant by adding it into the system. I have no idea if this even works?

Also, there's another radiator that has a bright green-blue discolouration around the copper valve - I think it's oxidation. I'm not sure if that can be caused by a leak though? The other radiators don't have this discolouration though. Wdyt?

Thank you for your suggestions.

 

[mgrover]

"Also, there's another radiator that has a bright green-blue discolouration around the copper valve - I think it's oxidation. I'm not sure if that can be caused by a leak though? The other radiators don't have this discolouration though. Wdyt?"

thats probably the leak.

 

[Lacan07]

I thought you could get some kind of sealant that you add to the system and flush it through? This might fix small leak.

 

[fernicarry]

No guarantee new pipework will be perfectly leak free either. Plumbers just don't work to that level of detail...

Put some Fernox F4 in it and see what happens. You can add it through the filling loop same as you would inhibitor. Topping up twice a year is a bit more frequent than you wold like but so long as you also keep the inhibitor up to strength it should be fine.

 

[lizziecupcakes]

"Also, there's another radiator that has a bright green-blue discolouration around the copper valve - I think it's oxidation. I'm not sure if that can be caused by a leak though? The other radiators don't have this discolouration though. Wdyt?"

thats probably the leak.

I really have no idea.
I'm just wondering if it is? Is it something you have experience with?

I thought copper pipes can discolour to that green-blue colour naturally, but I wasn't sure if it can be caused by a leak too.
Does anyone know for sure?

 

[lizziecupcakes]

No guarantee new pipework will be perfectly leak free either. Plumbers just don't work to that level of detail...

Put some Fernox F4 in it and see what happens. You can add it through the filling loop same as you would inhibitor. Topping up twice a year is a bit more frequent than you wold like but so long as you also keep the inhibitor up to strength it should be fine.

Thanks!
What inhibitor brand could I use?
I have no idea how much to use to keep the inhibitor up to strength though.

Also, we had someone do the yearly boiler check recently (annual service i think my partner sorted - I am not sure myself) but he didn't add anything to the system. Was he supposed to?

My partner confirmed he didn't add anything to the system - he just did a "safety check", cleaned a few parts, checked the boiler itself, turned on the system. Not much else.

 

[Cubist]

Combi boilers handle expansion of the water via an internal expansion vessel and the excess is then drained outdoors. As a consequence a small amount of air will form when the water cools and an air bubble can become trapped in the highest radiator. This is normal and the unwanted air bubble can be easily bled off from that radiator. Periodically it can become necessary to manually top up the CH water system as this is not an automatic function.

The simplest and best approach to test whether a valve or pipe is leaking is to wrap the suspect pipe or valve in some toilet tissue while the CH is running. If it does not get wet than there is no leak.

Discolouration of the copper pipes and fittings can occur through simple oxidation in the atmosphere but this is a fairly slow process and easily dealt with using a little metal polish. Green and bluish discolourations though can also be caused by a failure of the plumber to properly and thoroughly clean off any excess flux used in the soldering process. When heated the flux material spreads out over the copper surface and aids the flow of the melted solder into the joint. Sometimes the melted flux can spread back along the pipework and if it is not cleaned away can accelerate the oxidation process. Again, a metal polish can be used to remove the oxidants and thus prevent the problem in the future.

Over heating the copper during the soldering process can also cause the metals base colour to change. This usually can't be removed - don't be tempted to try to polish such discolouration out of the metal, you can weaken the walls of the tube.

 

[paulc]

I thought copper pipes can discolour to that green-blue colour naturally, but I wasn't sure if it can be caused by a leak too.

A pinhole leak could result in a build up of green ick (verdigris). Another cause is the remains of plumber's flux slowly attacking the copper and causing a pinhole leak to appear.
When I do any soldering on pipework, the joint gets a wipe down whilst still hot. Then I'll give it a good clean with some water that has a good dose of Bicarb of Soda added. This neutralises the acidic nature of any remaining flux and stops the formation of verdigris.

Pretty sure I'd suggested a leak sealant last time you raised the subject. Fernox is a market leader in central heating additives so you can't go wrong using their stuff. Don't bother with the pressurised canisters. Much easier to isolate the magnetic filter, unscrew the bowl, tip the chemicals in to it, and then screw back in place.

 

[lizziecupcakes]

The simplest and best approach to test whether a valve or pipe is leaking is to wrap the suspect pipe or valve in some toilet tissue while the CH is running. If it does not get wet than there is no leak.

I'll try this!
But it might evaporate off the tissue. I'll probably have to go round checking every few mins with my partner.

 

[Cubist]

If the pump is running when you wrap the tissue it should take less that a minute or so for any leak to become apparent, Leave it longer then yes theres a risk that the heat will dry the tissue but you may still see the stain on its surface.

 

[montyjohn]

For the record, my gas combi in my previous had to be topped up about three times a year. I just kept an eye on it and didn't think much of it. But it was a three bed ex-council semi so wasn't too concerned about a bit of moisture wherever it was.

This went on for 13 years, boiler was fine. Never saw any damp spots.

From my research at the time one possibility is a defective expansion vessel. If it's low on pressure, then when water expands it will max out and you lose water through the overflow. This would happen on every cycle slowly lowering the pressure.

The leak could be in the boiler. In summer you could isolate the CH pipework form the boiler (assuming you have valves) or get valves fitted (easy DIY job) and close them off. With the system now having a very much reduced volume of water if the boiler does have a leak, it should be noticeable on the gauge in a day or two (assuming your valves work well).

If you know it's on the network somewhere and you are really really determined to find it, you could add valves on different branches of the system to isolate them and then monitor how the boiler gauge changes. Close off the radiators on the remaining radiators to make the response quicker. A lot of effort though. But could be a fun project. May drive you mad.

 

[fernicarry]

What inhibitor brand could I use?

Fernox make inhibitor as well. There will be some guidance on the can as to size of system it treats. I imagine one can is plenty for all but the biggest systems. I don't think there is any harm in having too much of it.

 

[lizziecupcakes]

May drive you mad.

haha. This house is already driving me bonkers.
I'm still doing it... but i am at a point where the love in "labour of love" is disappearing lol.

 

[Flyfisher]

I have a Valliant ecoTech boiler and I also find that the system can lose pressure, though I'm not entirely sure about how. This is because I've never noticed a gradual loss of pressure but more of a sudden loss if I'm away for a while and the boiler has not been operating.

This has become even more irritating over the past 18 months or so since I've added the ability to control the system remotely (as well as other things, using Home Assistant) so that when I'm soon to arrive home after being away, I remotely switch on the system but still arrive at a cold house because the pressure has dropped and the boiler won't start. It's an easy fix to then add some pressure and the boiler fires up straight away, but that's not really the point! There's no obvious leaks at the radiators or UFH manifolds, though of course not every bit of pipework is visible so I can't be entirely sure, but my feeling is that I should have noticed a pressure drop if there is a leak somewhere, yet I only seem to have this problem after being away for a while and boiler has been idle.

 

[Stevers]

When our central heating was installed Drayton TRV valves were fitted on all but one radiator. Many of these obviously leaked with the failures indicated by the green verdigris round the glands and even running down the pipes. Drayton themselves suggested that they had been part of a bad batch and sent me a supply of the required gland seals and the special tool to fit them. That solved the issue and was much less disruptive than draining down and fitting complete new TRV bodies.

Leaks on hot pipework aren't always obvious due to evaporation, so joints are best checked when cold, but deposits can be a giveaway.

 

[a twig]

I have a Valliant ecoTech boiler and I also find that the system can lose pressure, though I'm not entirely sure about how. This is because I've never noticed a gradual loss of pressure but more of a sudden loss if I'm away for a while and the boiler has not been operating.

This has become even more irritating over the past 18 months or so since I've added the ability to control the system remotely (as well as other things, using Home Assistant) so that when I'm soon to arrive home after being away, I remotely switch on the system but still arrive at a cold house because the pressure has dropped and the boiler won't start. It's an easy fix to then add some pressure and the boiler fires up straight away, but that's not really the point! There's no obvious leaks at the radiators or UFH manifolds, though of course not every bit of pipework is visible so I can't be entirely sure, but my feeling is that I should have noticed a pressure drop if there is a leak somewhere, yet I only seem to have this problem after being away for a while and boiler has been idle.

Vaillant ecoTechs always have fun and games with pressure sensors. My 4 year old boiler has had 2 replacements under warranty and my previous had 3 replacements under warranty in 7 years.

The sensor that drives the display externally is different to the one the boiler uses to control itself, so what we were seeing as 1.2 bar the boiler was seeing as much higher and then would periodically have a flap and dump everything out - reset the boiler and re-fill and it would be fine for a while. Similarly was always worse when boiler had been idle for a while.

Vaillant people don’t even argue the toss when I book the appointments, they just come out and swap in new ones - all done in 30 mins usually

 

[my_name_is_slim_daisy]

I also have a Vaillant EcoTec and experiencing pressure fluctuations. I’m topping up 2-3 times a year.

In what order would you use Fernox F4 vs F1. Presumably F4 first, but how long should I wait before dispensing the F1?

 

[my_name_is_slim_daisy]

Don't bother with the pressurised canisters. Much easier to isolate the magnetic filter, unscrew the bowl, tip the chemicals in to it, and then screw back in place.

@paulc thanks for the info. Is there a reliable YouTube video I can follow on how to do dispense Fernox F1/F4? I’ve watched a couple and it seems to involve acquiring the right threads, attaching the nozzle to the filter, opening the valve to check for leaks…. And if there’s a leak then use tape on the thread to tighten the connection… test for leaks again.. and then dispense! If this is normal, great! But just want to make sure I’m following a good step-by-step guide. Very nervous about dispensing this stuff and burning the house down just before Xmas

 

[paulc]

If the top of your magnetic filter unscrews, leaving the body attached to the pipework, follow this video:

or:

If your filter is like mine and the bowl unscrews (leaving the top attached to the pipework), you can follow the same steps as above, but no need to suck the water out.

 

[fernicarry]

attaching the nozzle to the filter, opening the valve to check for leaks

I think you're referring to attaching to the filling loop. All systems have a filling loop, not all have a magnetic filter. If it looks like the link then nothing to acquire. If you do have a magnetic filter as @paulc says its even easier and you can buy the inhibitor in a cheaper container.

Close the two valves at the ends of the flexible hose (lever at right angles to the hose) (at least one of them should normally be closed). Unscrew the end of the hose farthest away from the boiler pipework using the metal "wings". The water left in the short section of hose will come out but it will be a tiny amount. Attach the hose to the can. Slowly open the valve on the pipework side. If no leak then pull the trigger to discharge the can. Once can is empty close the valve again. Unscrew the can. Reattach the filler hose to the water main side. Top up as needed. I don't think the can leaking is a high risk unless you are really cack handed at attaching the hose. If anything goes wrong just close the valves and seek help.