Expansion Vessel Replacement & Repair

Replacement is the correct fix once the diaphragm has split. We isolate and drain the vessel, remove it, fit a correctly sized replacement with a new isolating valve and flexible connection where needed, pre-charge it to the system design pressure and refill, vent and test the system. Central heating expansion vessel replacement and boiler expansion vessel replacement are both routine same-day work for us.

• Correctly sized vessel selected for system volume
• New isolating valve and connections fitted
• Pre-charged to design pressure before refill
• System refilled, vented and pressure tested

A failed expansion vessel shows itself through pressure that climbs sharply when the heating runs and falls back when it cools, a pressure relief valve discharging outside, or repeated boiler lockouts. Expansion vessel diaphragm failure is confirmed by water discharging from the Schrader valve when depressed — that is the water side leaking past the split diaphragm and the vessel cannot be repaired.

• Diaphragm failure confirmed at the Schrader valve
• Pressure behaviour logged across a heating cycle
• PRV discharge and lockout faults diagnosed
• Written quote before any chargeable repair

A waterlogged expansion vessel — one full of water with no air cushion left — leaves nowhere for expansion to go, so the system pressure spikes every time the boiler fires. Where the diaphragm is intact we drain and recharge; where it has failed we replace. Either way the system is retested through a full heating cycle before we sign off.

• Drain-down and recharge where the diaphragm is sound
• Replacement where the vessel is beyond recharge
• Full heating cycle retest after the work
• Advice on preventing recurrence

An expansion vessel leaking from the shell has corroded internally and must be replaced — patching is not safe on a pressurised vessel. An expansion vessel valve leaking at the Schrader core is often a simple core replacement, and a weeping connection is usually a failed olive or fibre washer. We identify which of the three you have before quoting.

• Shell corrosion assessed for replacement
• Schrader valve core replacement
• Connection, olive and washer renewal
• Pressure hold test after every repair

Where the boiler’s internal vessel is too small for the system, or there is no room to service it, we fit an external expansion vessel on the return pipework with its own isolating valve and drain point. This is a common upgrade on extended heating systems and older properties with large radiator volumes, and it makes every future service far quicker.

• Sized from total system water volume
• Isolating valve and drain point fitted for easy servicing
• Wall or floor mounted with proper support
• Commissioned and labelled with pre-charge pressure