Central Heating Pumps and Circulation Problems

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Central Heating Pumps and Circulation Problems

What the pump does, symptoms of failure, replacing one and efficiency rules

A circulating pump is the component that moves hot water around a heating system, and its failure produces symptoms that are frequently blamed on the boiler.

What it does

Pushes heated water from the boiler through the radiators and back. On most systems it runs whenever heating or hot water is called for, and a failing pump means heat is produced and not distributed.

Symptoms of a failing pump

Radiators cold while the boiler is clearly running and hot. Noise — humming, grinding or vibration. The pump body hot but the pipes either side not warming. Heating working intermittently.

Air in the system and sludge cause similar symptoms, so bleed radiators and check the system pressure before assuming the pump.

Sludge is the usual underlying cause

Corrosion products build up over years, block the narrow passages and wear the pump. A power flush and a magnetic filter, with inhibitor added to the system water, address the cause rather than the symptom.

Fitting a magnetic filter is one of the better investments in an older system.

Efficiency requirements

Modern circulators must meet an energy efficiency index under EU and UK rules, which in practice means variable speed rather than fixed. These use substantially less electricity and adjust flow to demand.

Check the head and flow rating required for your system rather than buying on price.

Replacing one

It involves isolating and draining part of the system and working on a wet, electrically connected component. Unless you are competent and know the isolation points, this is a job for a heating engineer.

Anything gas-related must be done by a registered engineer by law.

Balancing radiators

If some radiators are hot and others lukewarm, the system may need balancing — adjusting the lockshield valves so flow is distributed rather than taking the easiest path. It costs nothing and is frequently the actual fix.

Bleed radiators at the start of the heating season, and check the system pressure afterwards.

When to call someone

Any smell of gas, any boiler fault code, water leaking from the boiler, or a system losing pressure repeatedly.

Making a system more efficient

Thermostatic radiator valves, a room thermostat and a correctly set boiler flow temperature between them save more than any component swap. Many condensing boilers run at a flow temperature far higher than they need.

Lowering the flow temperature lets a condensing boiler condense, which is where its efficiency comes from.

Insulation first

Loft insulation, draught-proofing and cylinder jackets pay back faster than anything inside the heating system.

Prevention

Annual servicing, inhibitor levels checked, and a filter cleaned each year.

WHERE TO BUY

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