Boiler problem

[Symposium]

My combi boiler keeps losing pressure. It's still giving hot water but I noticed the gauge on zero so called out a Hometree. They send an engineer initially just topped up the water. I explained that I knew how to do that but wanted to know why the pressure had dropped as surely something must be leaking. We went round the house checking the pipes etc but nothing is showing. He said to call him out again if the pressure dropped. 2 days later sure enough the pressure was gone so I called him back. We checked everything again but there's no sign of water anywhere. He says that it may be an internal leak and if so we need a new boiler. He's left me to keep topping it up and checking for leaks over the next week. I'm wondering if I need a second opinion? Not sure if hometree would send anyone else but I'm concerned that he can't confirm what the problem is. He says there is no test for it as it's an old boiler and he can't isolate the part he would need to test. He hasn't looked inside the boiler but perhaps that's normal for this kind of issue.

I am not a heating engineer, but we had a similar problem, so on the off chance this might help.

We had a Grants combi oil boiler kept losing pressure, no heat or hot water. Loads of plumbers came out, eventually found out it was the diaphragm in the expansion vessel had gone. They kept changing it, but it kept failing. In the end we had an old guy come and he scratched his head, and said the only thing he could think of was fitting an additional external (to the boiler, not outside the house) expansion vessel. Looked a bit weird, but it worked and had no trouble for 15 years until we moved.

I had something similar - it was letting water out through the condensation pipe externally, so it wasn't really a noticeable leak. But it was just some kind of valve that needed replacing and was a cheap, easy fix.

TBH sounds odd that the guy can't find the problem - Engineers should be able to find the problem, even if they ultimately answer that the boiler is so old replacement parts aren't available. What kind of boiler engineer doesn't even look inside the boiler? (I don't know what a Hometree is)

Have you tried venting all the radiators?

We had this too, it was down to a tiny leak in a pipe under the floorboards

I'm thinking unlikely to be a leak in pipes/radiators as they are all surface mounted and quite visible and we can't see anything. I'm feeling like it's probably an internal leak but unsure why the engineer can't look inside and see if there's a faulty part to replace? He's just saying we'd need a new boiler.

Had the same years ago in our old house. Engineer said it could be two things, a valve or a leak on the expansion vessel Changed the valve first as cheaper, but it was the expansion vessel. I don't think it was that cheap for a new one, but far cheaper than a new boiler

If it's the expansion vessel, try not to panic. You can still get hot water safely and won't need the heating on for 2-4 months. I know this as there qas a stock shortage and then suppliers closed over Xmas.

Do you have a condensate pipe on the outside wall of boiler or nearby? If so, and it's dripping occasionally, that's your problem.

I think you need a second opinion.

Check round every radiator, valves in and out, all associated pipework. Is the pressure relief valve not dripping? This is the blow off pipe usually on the outside wall but on some they're teed into the condensate.

He did check the outside pipe and it looked dry. He also ran a little test that involved waiting for a pipe under the boiler to collect water in a cup . That didn't show anything either.

I think I'll ask hometree if I can get a second opinion and take it from there. At least we still have hot water.

Thanks for all the responses!

The expansion vessel is a possibility.

Other than that you can get leak detection firms that put a dye in the water and see it with special cameras if its leaking.

We’ve had this for well over a year now and kept “making do”, however a new boiler was what was needed and it was the best thing we did! Better heat in the shower, better for the radiators etc (had a bigger boiler fitted to accommodate all new radiators we’ve added over time) and is money well spent. We also asked for another expansion vessel fitted. Hopefully, this will last us many years now!

How old is the boiler ?

If it is say less than 10 years old I would say maybe worthwhile repairing.

If it is 15-20 years old it has probably had its day and may well need more expensive repairs in the future. I don't know for sure but I would guess it is the hot water side that is more prone to needing repairs, so the fact that the heating circuit has gone is a clue that maybe you are in for more expensive work in the near future.

Also look at the boiler efficiency and boiler make/type. If it is a cheap old boiler the efficiency may be well down on a modern one. That won't pay for the new one in a short time period, but should make a dent in the cost.

Boiler was in the house when we moved in so not sure of the age but we think 15 years at least. It's a decent Worcester Bosch. I've been in touch with Hometree this morning and they say they cannot help me anymore! They are even refunding my call out fee. The engineer has sent a report that does not mention a possible internal leak but suggested a hidden leak in pipe work that requires trace and access. There is only one area of hidden pipe work as most is surface mounted. Unfortunately I don't have a good enough home insurance policy to cover this, I've been in touch with them and they will only cover a claim after I have had the problem fixed myself!(less the excess) . I am going to contact a local gas engineer/plumber that I have used before and hope that he can help me!

I guess if they think it is an internal leak spending money on a new boiler would be pointless.

Money better spent probably uncovering the internal leak in the pipework.

I would inspect all the radiators very carefully. The water has to be going somewhere. Maybe thermal imaging could help you with the leak, it has helped me with the piepwork in my house, but really depends how much water is coming out - it doesn't take a huge amount to drop the pressure normally.

I'm just a bit puzzled as I've gone round and checked every bit of pipe work and radiators and cannot see anything damp. There's literally only one small section of board in pipes on my landing leading into the bathroom behind the bath . It could be checked if we remove the bath panel I think. But there's nothing showing in the kitchen underneath. we've previously had a tiny leak under the bath that showed up by puddles in the kitchen. So you'd think we would see something.

Probably best to remove the panel and check if you can. It is normally possible to pop them out.

It can take some time for leaks to make it through the plasterboard because they have to get through the floorboards and onto it first. So it depends for example where the joins in the floorboards are relative to the leak. Then work their way through onto the plasterboard.

But if it is leaking on the plasterboard it will make it through eventually. Then you will get another bill for replacing the plasterboard or covering up the mess it makes as the plaster bubbles.

If you have auto venting valves on the radiators, you will get a pressure drop as they activate. Normally the drop is very slight, but in theory could be greater if there is a lot of air in the system.

As I suggested earlier it's worth venting all the radiators to remove the possibility of the pressure drop being caused by the auto venting, even if unlikely.

Sorry didn't mean to ignore your advice about radiators. Would that happen even though the heating is not in use right now and all radiators cold?

The bath panel is sealed in with sealant unfortunately, so I'd rather not touch it unless essential. It's already been taken off once a few months ago when we had a leak under there.

We have thermostatic valves on the radiators , they were fitted a couple of years ago. I've been in touch with a local gas engineer that I've used once before. He says he probably can't come out until next week so I'm trying to decide if I wait for him or try someone else.

We had same issues and it turned out to be a thermo coupling. Part only cost a few quid and it was fixed relatively cheaply. That was over 20 years ago though, but still combi boilers are quite simple

Definitely worth getting an independent engineer out, a 15yo Bosch can still be a good boiler and given an expansion vessel is far less than a new boiler, worth considering a repair, might not even be that, our engineer tested the vessel in situ i believe.

Funny he told you a new boiler is required but in the report said it was a leak in the pipe work.

Yes I'm very confused about his report as he definitely said an internal boiler leak was possible and that meaning a new boiler was a necessary.. But he only wrote about a hidden pipe leak being the cause.

Without proper testing, unless your boiler is from the stone age, how can he tell?
Could just be a 10p seal on a pipe coupling for all he knows.

Sounds like he is on a bonus scheme for boiler replacements!

I know labour rates are high but an expansion vessel for CDi Greenstar Bosch boiler is about £100 - £200, model dependant, a new boiler will be around £3k, i know what i'd be look at.

I don't understand the benefit to him to do this. It has been left me to deal with it, they are not trying to sell me a new boiler or anything. It's seems they are just not interested in helping me but have said I should get leak detection as that's all he has suggested in his report.

Has to be worth checking under the bath, so you've confirmed/eliminated that. Also, you could top the pressure up to within normal range (tend to have our WB filled between 0.8-1.2). Then put heating on - our current boiler rises about 0.4 when on, our old house was around 0.5 rise. If it goes over 2 bar that might indicate the expansion vessel - ours would run at around 3.2bar when we had this problem.