Glow Worm Flexicom 18 - Now It's The Pressure...

SaabmanBOF · 7 Oct 2018 at 08:30

The boiler is a Glow Worm Flexicom 18 SX. To set the scene, there's a slight leak somewhere in the heating. No signs of leakage visible anywhere, and I've even had the hydrogen leak detection boys out three times so far; they can't find it either! It's obviously opening up when the system heats up, and closing when it cools down. I may try a power flush next; SOMETHING must work...

To keep the water loss down, I run the boiler at low pressure - not above 1.0 bar cold. It dropped from 0.9 to 0.6 over four months during the summer, when I was running only the hot water for an hour a day, but with the heating going as well now the loss is more - about 0.1 bar per day.

It would drop to 0.5 bar previously, as per the spec, before I got the F9 code, but now I get F9 at 0.7 bar on the display.

Replace the pressure switch (easy and cheap)?

Call an engineer (easy but not cheap)?

Does anybody have any idea what might be wrong?

Hedge · 7 Oct 2018 at 08:59

I have a Worcester Green star doing exactly same thing. I was convinced the heatex was leaking and it was losing water through condensate. They changed heatex (supposedly. I was at work) and it seemed better for a while but now it's doing it again.

Had the whole summer of not needing to top up pressure. Then now within a few days it's hit zero.

a1ex2001 · 7 Oct 2018 at 09:28

Have you tried any of the leak stop adatives? They can be pretty effective against slow hard to find leaks.

Kol · 7 Oct 2018 at 11:21

a1ex2001 said:
Have you tried any of the leak stop adatives? They can be pretty effective against slow hard to find leaks.

Interesting. This gets glowing reviews https://www.screwfix.com/p/fernox-f4-central-heating-leak-sealer-500ml/45902

https://www.screwfix.com/p/sentinel-internal-leak-sealer-1ltr/99730

Hedge · 7 Oct 2018 at 22:08

Used the fernox leak sealer last year and it seemed to work well but I think it coincided with the warmer weather and we were using the heating less anyway.

I'll put more leak sealant in next week and hope it improves.

tom_nieto · 7 Oct 2018 at 22:38

Interested to see how you get on. Our glow worm combi is behaving in exactly the same way. Had our friendly gas engineer out who suggested a couple of things like replacing the pressure release valve and potentially the expansion chamber. He re-pressurised the expansion vessel while he was there which doesn’t seem to have made too much of a difference. No visible leaks or air locks in the radiators. God help us if the underfloor heating has a slow leak!

SaabmanBOF · 9 Oct 2018 at 11:55

It's not the leak I'm bothered about; I know what that is, just not where it is... I'll consider putting in a leak stopper, but my plumber reckons they're more of a way of buying time than a permanent repair, and because of the small size of the water passages in the heat exchanger, I'm concerned about the possibility of restricting them and causing more problems.

By the bye, does an adequate amount of inhibitor in the system prevent the formation of scale in the heat exchanger? I live in a very hard water area, and every time I top up the system, I'm adding a little more calcium to the circulating water.

The F9 at 0.7 bar is more of an immediate concern. I've ordered a new pressure sensor and will fit it tomorrow, but I'm not all that hopeful that it will solve that problem.

NvidiaDan · 9 Oct 2018 at 17:04

Inhibitor does protect again limescale but like you have said it's not ideal to keep introducing fresh water like you are having to at the moment.

Pabl0 · 11 Oct 2018 at 13:02

Why not fit an inline scale reducer to the cold feed into the boiler.

SaabmanBOF · 13 Feb 2019 at 20:48

I tried the Fernox leak sealer last Spring, and the system held pressure for a week or so, then started to drop again, and was soon as bad as before. This time I spoke to a technical guy at Fernox, who assured me that the sealer would not block the heat exchanger passages, confirmed two bottles was the right amount, and told me to run the system for a good few hours after adding the sealer. I ran it for three or four hours the first time.

I did the job on January 23rd, and ran the system continuously, with the 'stats set to max so the house never reached temperature, for 24 hours; just as well it was in a cold spell of weather. It has stabilised at 1.1 - 1.2 bar cold, depending on the ambient temperature, and hasn't dropped in three weeks, despite another cold snap and getting plenty of use.

The key seems to have been running the system for a good long time to allow the seal to form. Fingers crossed, it's a permanent repair; if this thread is resurrected, it wasn't...

Thank you one and all for your help.