Grant vortex combi boiler losing pressure

Neilhighlands · 3 Feb 2018

I have a Grant Vortex 26, and it is losing pressure. It can be at 1 bar in the evening, and be down to 0.3 bar in the morning. When the heating is on, it holds pressure, but as soon as you turn on hot water somewhere in the house the pressure drops. I thought the two systems were separate, but apparently not.
The adjustable valve (min, 1 2 3 4 5 Max) is leaking a bit. Not a lot, but a bit.
Can it be this adjustable valve, or something else? Any advice greatly appreciated.

Mike2007 · 3 Feb 2018

It could be the temperature adjustment valve inside the boiler. If it's leaking on a joint fix it, if it's leaking on the body change it . I had a Worcester Bosch boiler that was gaining pressure because it was leaking across the flat plate heat exchanger( could be opposite on yours). On combi's they usually get annoying leaks around these components.

Terrywookfit · 3 Feb 2018

The TMV has nothing to do with system pressure.
Is the PRV discharging water?

oilboffin · 3 Feb 2018

Could be expansion vessel lost charge and it's offloading like T said. If so if it's been going for a while the PRV may need replacing.Bob

Neilhighlands · 4 Feb 2018

The TMV has nothing to do with system pressure.
Is the PRV discharging water?

There is a very slight leak on the PRV itself. It’s not discharging any water out the pipe, but is leaking a bit. The plumber didn’t think it was leaking enough to cause the drop in pressure.

Neilhighlands · 4 Feb 2018

Bob, I just had a new expansion vessel fitted. Doesn’t seem to be leaking anything. This was the first thing the plumber thought was responsible for the pressure loss so replaced it.

oilboffin · 4 Feb 2018

You could tie a plastic bag on the pipe from the prv and that will tell you if it's leaking and any leak inside the boiler will drop the pressure.Bob

oilboffin · 4 Feb 2018

By the way the first thing to do is not to replace ex vessel but to check the charge pressure and pump it up cheaper than a replacement.Bob

Neilhighlands · 4 Feb 2018

Hi Bob, thanks. As as said above, there is a small leak at the PRV. Not through the pipe, but actually where it is mounted. It is only a very small leave. Do you think it could be responsible for the pressure loss?

Neilhighlands · 4 Feb 2018

Just had a thought. Does a new expansion vessel need to be pumped up? Or does it come at the right pressure? If it needs to be pumped up, to what pressure?

andytw · 4 Feb 2018

Just posted on a similar thread, my neighbours Grant boiler was losing water from the PRV. I checked the expansion vessel and changed the PRV.
Same problem, so reluctantly swapped the expansion vessel then found the flexi hose on the expansion vessel was completely blocked so the expansion vessel was effectively not there at all. Fitted new hose. all OK

oilboffin · 5 Feb 2018

New hose or just clean out hose.Bob

Nihad · 22 Feb 2024

andytw said:
Just posted on a similar thread, my neighbours Grant boiler was losing water from the PRV. I checked the expansion vessel and changed the PRV.
Same problem, so reluctantly swapped the expansion vessel then found the flexi hose on the expansion vessel was completely blocked so the expansion vessel was effectively not there at all. Fitted new hose. all OK

Im having the same problem
The hose is gone all black

What type of hose did you use?

Exedon · 22 Feb 2024

Get the correct Grant part readily available try heating wold of spares around £15

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Grant vortex combi boiler losing pressure

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