Boiler pressure increasing mystery

Firefarie71

Hello all and thank you for reading this. 

We just bought a new home and a week after moving in, the boiler stopped working. When I checked, the error message said high water pressure. 

Its a Baxi Neta-Tec Combi GA 24. It's 11 years old. 

The water increases by 0.1 everyday when heating isn't on. We have to bleed the radiator every 4 to 5 days to lower the pressure.

Initial boiler engineer pumped up the Heating Vessel and replaced the PRV which cost £200. He said there was no issue with the filling loop. 

However, this didn't fix it and still increasing 

Different engineer came out who has previously serviced the boiler (he was on holiday when incident happened) and he also checked the filling loop which was dry when he unscrewed it. He didn't do anything but said its likely a cracked heat exchanger and time for a new boiler. Said it would cost around £400 to repair.

My OH is concerned we will spend £2.5k on a new boiler which may not fix this issue. We also don't want to spend hundreds of pounds on repairs if there is a chance other things may go wrong.  OH doesn't understand why pressure going up as where is the water coming from if the filling loop isn't leaking? 

Money is very tight as we ploughed all our savings into buying our home, so need to make sure we make an informed decision as we'll have to get a loan to pay for this.

I appreciate any advice from someone with a good knowledge of boilers. Thank you ❤️ 

Leethos

It does sound like a pin hole in the heat exchanger which is allowing the incoming cold to mix with the heating circuit and because the cold main has the greater pressure it’s adding charge to your heating circuit. You can test this by isolating the cold feed and seeing if the increase stops. It would however mean that you can’t use any hot water whilst running the test 

FreeBear

Firefarie71 said: My OH is concerned we will spend £2.5k on a new boiler which may not fix this issue. We also don't want to spend hundreds of pounds on repairs if there is a chance other things may go wrong.  OH doesn't understand why pressure going up as where is the water coming from if the filling loop isn't leaking?

I'm also scratch my head a little over boiler pressure increasing even when it isn't in use. If there is a crack in the P2P heat exchanger, I could understand the pressure increasing to match the mains water pressure. But it shouldn't go any higher when the boiler is cold. It might be worth booking a fixed price one-off repair with Baxi*. They charge £435 inc. VAT which includes labour and spares. If they can't fix, they'll only charge you a £90 call out fee.

If you want to stick with a Baxi, replacement boilers can be had for as little as £700 plus fitting. But modulation range is not brilliant, and you'd only get 2 or 3 year warranty. At the other end of the market, a Worcester Bosch Greenstar 4000 is about £1300 (10 year warranty and a 10:1 modulation range). My preference is a Viessmann 050 for around £1100 (again, 10 year warranty, and 10:1 modulation range). If you go to someone like Boxt, you'd probably get the WB or Viessmann for around £2300. A budget end Baxi is likely to be £1500 installed.

The alternative is to get a heat pump and do away with gas completely. You'd need to find space for a hot water tank and an outside compressor. Whilst it would (probably) cost a bit more than a top end gas boiler, you'd save £100+ standing charge. Now that the weather is warming up, there is no great rush to get a new boiler (or heat pump) installed - Washing can be done with a kettle of boiling water if need be..

*) https://www.baxi.co.uk/support/repairs#one-off-repair

Neilb1969

Worth double checking that the filling loop isn’t letting by. I had the same issue after a recent boiler service. Heating engineer said it was fine but it wasn’t. Open and close the filling loop valve a few times and see if it seals properly 

ritz55

I think I would second the filling loop as the issue. Easy test is turn off the tap for the filling loop and then disconnect it completely from the boiler, that way there is no chance of water going into the boiler via the filling loop.

If problem is still present then fixed price baxi policy will be the best option. I had a leaking heat exchanger a few years back and they come out and pretty much replaced every part in the boiler, while replacing the heat exchanger, any parts removed was replaced with a new part. 

WIAWSNB

Firefarie71 said:

We just bought a new home and a week after moving in, the boiler stopped working. When I checked, the error message said high water pressure.
Its a Baxi Neta-Tec Combi GA 24. It's 11 years old.
The water increases by 0.1 everyday when heating isn't on. We have to bleed the radiator every 4 to 5 days to lower the pressure.
Initial boiler engineer pumped up the Heating Vessel and replaced the PRV which cost £200. He said there was no issue with the filling loop.
However, this didn't fix it and still increasing 
Different engineer came out who has previously serviced the boiler (he was on holiday when incident happened) and he also checked the filling loop which was dry when he unscrewed it. He didn't do anything but said its likely a cracked heat exchanger and time for a new boiler. Said it would cost around £400 to repair.
My OH is concerned we will spend £2.5k on a new boiler which may not fix this issue. We also don't want to spend hundreds of pounds on repairs if there is a chance other things may go wrong.  OH doesn't understand why pressure going up as where is the water coming from if the filling loop isn't leaking?
Money is very tight as we ploughed all our savings into buying our home, so need to make sure we make an informed decision as we'll have to get a loan to pay for this.
I appreciate any advice from someone with a good knowledge of boilers. Thank you ❤️

As others, the only part that I'm aware of that can allow this to happen is the Plate-to-Plate heat exchanger. I know it can happen, 'cos it did on my GlowWorm, after I very cleverly used brick acid to clear out the sludge in a blocked one. Well, more than just sludge was removed from inside :-(

I'm struggling to find the exact model P2P for your boiler, but for most Baxis (and other makes), you can pick up reconditioned items (perfectly good - I've used them) for around £40 on eBay and other places. These have been professionally cleaned by reputable companies.

To replace it on the GlowWorm is a 30 minute job, so should be under an hour on yours - if you can find a plumber willing to fit a recon part (they should, whilst obviously declaring they won't be liable if it's faulty).

If you are 100% certain it isn't the filling loop (what kind is it? Can you leave one end disconnected?), then the P2P is the only other part I'm aware of that could do this. I don't think the Hydroblocs and diverters have both mains and system water running alongside?

So, possibly you can sort this with a friendly GasSafe and a recon part for, say, ~£150. But, it's clearly a gamble.

Example (but not certain it's your part): https://nationalboilerspares.co.uk/product/baxi-heat-exchanger-720776401/?

Firefarie71

Hi all

Thank you so much everyone for your comments and advice. 

I've removed the filling loop and put a container under the pipes. So far, after 2 hours, no drips. 

We're thinking of signing up to the 6 month  repair and care plan with Baxi. Its 73.98 month. We're thinking it will give us some time to save towards a new boiler.