Pump Failure / Circulation Issues
No water circulation in your wet underfloor heating? This guide covers pump diagnosis, freeing seized pumps, and knowing when replacement is needed.
Symptoms of Pump Failure
No water flow through manifold
Flow meters show no movement despite system calling for heat.
Manifold cold on supply and return
Both sides of manifold remain at ambient temperature.
Boiler firing but no heat delivered
Boiler runs and heats but warmth doesn't reach the floors.
No pump noise or vibration
Circulation pump is silent when it should be running.
Pump making unusual noises
Grinding, humming, or clicking sounds from pump indicating failure.
Step-by-Step Pump Diagnosis
Listen for Pump Operation
Put ear to pump when heating demands. Should hear humming/vibration.
Check Pump LED/Indicator
Modern pumps have status LEDs. Check manual for fault code meanings.
Feel for Vibration
Touch pump body when running. Should feel gentle vibration if operating.
Check Flow Meters
Observe manifold flow meters. No movement = no circulation.
Verify Power Supply
Use voltage tester to confirm pump receives power when demanded.
Try Freeing Impeller
If seized, use screwdriver in slot to gently rotate impeller shaft.
Common Causes & Solutions
Pump Seized After Summer
The most common cause. Pumps can seize when left idle for months during warm weather.
Solution: Try freeing the impeller by inserting a flat-blade screwdriver into the slot on the pump face and gently rotating. Run pump immediately after.
Electrical Failure
Pump motor has failed electrically, often due to age or power surges.
Solution: Check pump receives power. If power present but pump doesn't run, motor has failed. Replacement required.
Air Lock in Pump
Air trapped in pump head preventing impeller from moving water.
Solution: Open bleed screw on pump to release trapped air. Top up system pressure afterward.
Incorrect Pump Speed
Pump speed set too low for the system resistance, resulting in inadequate flow.
Solution: Increase pump speed setting. Most pumps have 3 speed settings. Try next speed up.
Blocked System / Sludge
Magnetite sludge has accumulated and is restricting flow through pump and system.
Solution: System requires powerflush to remove sludge. Magnetic filter should be fitted.
Faulty Pump Control
The pump is not receiving the signal to run from the wiring centre or controls.
Solution: Check pump receives power when heating is demanded. Trace wiring from wiring centre to pump.
Frequently Asked Questions
Need an engineer?
If this guide points to a fault you would rather not tackle yourself, our REFCOM-registered, F-Gas certified engineers cover London and the M25 with 24/7 emergency callout. Engineer time is £120 + VAT per hour with a written quote before any chargeable parts are fitted. Start with the relevant service below, or contact us for a site survey.