On an unvented cylinder service in Birmingham city centre, we checked the expansion vessel and found its diaphragm had failed: it wouldn't hold its air charge, and water came out of the air valve. We came back and fitted a new vessel.
We were in Birmingham city centre for an annual unvented cylinder service. While inspecting the cylinder we checked the expansion vessel above it and found the diaphragm inside had failed: the vessel wouldn't hold its air charge, and water came out of the air valve, so it couldn't simply be recharged. We returned on a second visit and replaced it with a new Aquasystem expansion vessel.
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Unvented cylinder repairs £99 for the first hour in office hours, parts quoted first. Immersion heater and vented cylinder repairs are quoted after a £99 diagnosis. Unvented cylinder annual service £120 (£90 with a boiler service).
No travel charge within 10 miles of B20 2JS. Further out, £2 per mile may apply — always agreed before anything is booked. Full price list
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We were in a flat in Birmingham city centre for an annual unvented cylinder service. Part of the service is checking the expansion vessel, the white tank above the cylinder in the first photo.
The vessel's diaphragm had failed. It wouldn't hold its air charge, and water came out of the air valve, which means the water had got through to the air side. A vessel in that state can't be recharged: it has to be replaced.
We returned on a second visit and fitted a new Aquasystem expansion vessel in its place. The second photo shows the old vessel and the new one side by side. Our unvented cylinders page covers servicing and repairs.
The annual unvented cylinder service is £120, or £90 when it is done with a boiler service. An unvented cylinder repair is £99 for the first hour, with parts quoted. Details are on our price list.
When the water in the cylinder heats up, it expands. The vessel has an air charge on one side of a rubber diaphragm, and it takes up that extra water so the pressure in the system doesn’t climb.
A vessel that has just lost some air can be recharged, and that is a routine part of the annual service. If water comes out of the air valve, the diaphragm has failed and the water has got to the air side, so the vessel needs replacing. That is what we found here.
Without a working vessel, the expanding water has nowhere to go, so the system relies on its safety valves to let water out. It needs putting right, not living with.
The annual unvented cylinder service is £120, or £90 when it is done with a boiler service. An unvented cylinder repair is £99 for the first hour, with parts quoted.
Job attended and photographed by our engineers, November 2026. Written up by Saeed Iqbal, the engineer who leads Synergy Gas & Plumbing (Gas Safe registered 594385). More of our work in the city is on our Birmingham page, and every job we write up is on the case studies index.
Service £120
Annual service £120 (£90 with a boiler service). Repairs £99 for the first hour in office hours, parts quoted first.
No travel charge within 10 miles of B20 2JS. Further out, £2 per mile may apply — always agreed before anything is booked.
The vessel was hanging off its pipework because the backboard had only been nailed to plasterboard with no stud behind it. We fitted plywood across a wider area with heavy-duty fixings and remounted it.
Read the case studyA tenant called with no hot water and asked for both immersion elements to be replaced. We drained the cylinder down, took out two scaled and corroded elements, fitted new ones and tested them. Hot water back the same visit.
Read the case studyA heat interface unit in a city-centre flat had stopped giving hot water. We traced it to the flow switch, ordered the correct part, came back and fitted it. Tenant back in hot water.
Read the case studyA G3-qualified engineer, £99 first hour on repairs in office hours, £120 for the annual service. Call or WhatsApp a photo.
