Twin Impeller Shower Pump Repair London

How a twin impeller pump fails

A twin pump has one motor driving two impellers, one on the hot feed and one on the cold. When a shower suddenly runs cold or scalding, one impeller has stopped contributing — usually because that side has drawn air, the impeller has seized, or debris has jammed it. Because the motor still runs and one side still works, the pump sounds normal, which is why the fault is so often misread as a shower valve problem. Isolating each side and measuring the flow settles it in minutes.

• One-sided failure causing temperature swings
• Air drawn into the hot feed from the cylinder
• Seized or jammed impellers on either side
• Debris from the cold tank blocking the strainer
• Failed flow switch on one feed
• Worn bearings and mechanical seal leaks

Hot side problems and cylinder connections

The hot side is the usual casualty because it is the side that can pull air. A hot feed taken incorrectly from the cylinder, an Essex or Surrey flange that has been omitted, or a cylinder that has been allowed to run low will all let the pump draw air rather than water. We check the take-off arrangement at the cylinder and correct it where it is wrong, because no amount of pump repair fixes a hot feed that is designed to gulp air every time the cylinder level drops.

• Cylinder take-off and flange arrangement checked
• Hot feed re-routed where it draws air
• System vented and re-primed properly
• Cold storage capacity assessed against demand

Negative and positive head pumps

Positive head pumps rely on gravity pressure to start and need the cold tank above the outlet by a specified distance. Negative head pumps have their own sensing and can be used where the tank is level with, or below, the shower. Fitting a positive head pump on a negative head installation produces a pump that will not start reliably — a fault we see regularly in loft conversions where the tank was moved. We confirm the head arrangement before advising a repair or replacement.

Repair or replace a twin pump

Impellers, seals, bearings, switches and brass ends are replaceable on most twin pumps, and repair is usually the sensible route. Replacement is right when the motor has failed, when corrosion has attacked the pump body, or when the pump is the wrong type or duty for the installation. In all cases we correct the installation issues — flexible hoses, isolation valves, strainer access, anti-vibration mounting — so the replacement does not fail the same way.

• Impeller, seal and bearing kits fitted
• Correct head type and duty confirmed
• Flexible connectors and isolation valves installed
• Strainers made accessible for future servicing