Plumbing

Grant Oil Combi 90 Mk2 - Rising boiler pressure issue.

Anonymous user 17/03/2024 - 11.46 AM

Hoping some of you fine people can offer me some advice! We inherited Grant Combi 90 Mk2 Oil boiler with our house. It’s fairly old, guessing 15 years plus and has been a continuing money pit over the last 4 years. We’ve resigned ourselves to a new boiler soon and are saving but the current issue is as follows and any advice which means I can minimise potential diagnosis/parts costs would be very much welcomed and appreciated! Oil tank was refilled recently. Was low but definitely not out. Heating and hot water appeared absolutely fine and functioning normally. Next day I noticed the pressure gauge up to 2.5 bar (usually rests around 1.2, about 1.6-1.8 when active). I switched the system off. Cooled and drained and checked the usual suspects. Expansion Vessel was fine, holding 1 bar, no signs of water ingress. PRV seems fine and functioning as it should. I did find two leaks subsequently. One on pipe elbow from the PRV and one on the cylinder side of the filling loop, both the flexible hose and valve dripping. These have both been repaired/replaced and there are no more leaks. However the rising pressure issue is continuing regardless. Whether the boiler is switched on or off, over the course of a few hours, the pressure level slowly rises to 2.5 bar. My instinct is that it’s water ingress somewhere in the system. The diverter valve or the Heat Exchanger is my best guess? The Diverter valve had the internal components changed about 2 months back and the Heat exchanger was replaced about 2 years ago. I’m leaning towards the Heat exchanger but it’s just a best guess. Could any of you fine experts offer some more educated clarification or suggestions please. Many thanks.

1st Class Gas

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Glasgow

Hello, Congratulations on your new arrival! Not getting much sleep, I imagine. Your own diagnostic of hex could be correct. However, there are a few other bits before that. What about filling loop, is that connected, could be passing. Expansion vessel holding pressure, that's good, but there may be a blockage between that and the system meaning vessel is effectively not even doing anything. Best advice is get a qualified engineer out to look at it. May very well be a no parts required fix and you are safe in the knowledge its been checked for safety and integrity, with the correct tools and skill set. Good luck, Dunc

Answered16 March 2024

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