Central heating repairs

The short answer

Most heating complaints come down to air in the system, sludge restricting flow, a failing pump or motorised valve, or controls that were never set up correctly. Radiators cold at the bottom point to sludge; cold at the top points to air. A system flush, a magnetic filter and correctly configured controls resolve a large share of problems without replacing the boiler.

What the work involves

Balancing radiators, bleeding air, chemical or power flushing, fitting a magnetic filter and inhibitor, replacing pumps, motorised valves and thermostatic radiator valves, and upgrading to zoned or smart controls.

Rules and consents in Scotland

Gas boiler work requires Gas Safe registration. Electrical connections to controls should be carried out by a competent electrician. Adding controls and zoning is encouraged under Scottish energy standards on system replacement.

What commonly goes wrong

Replacing a boiler on a heavily sludged system without flushing it, which can void the warranty and damage the new heat exchanger quickly.

What it usually costs

Indicative ranges only, to help you judge a quote. They are not an estimate for your property — only the business doing the work can give you that.

• Balancing and bleeding is a short labour-only job.
• A power flush is priced per radiator and is a moderate one-off cost.
• Pumps, motorised valves and TRVs are individually inexpensive parts with a labour charge attached.
• Zoning and smart controls cost more but usually pay back through better control of heating in a large or period property.

What to do, in order

1. 1Note which radiators are cold and whether at the top or bottom.
2. 2Bleed radiators and check system pressure before calling anyone out.
3. 3Ask for a flush and inhibitor if the water drawn off is black.
4. 4Fit a magnetic filter to protect the system going forward.
5. 5Balance the system so distant radiators heat properly.
6. 6Set controls and TRVs deliberately rather than leaving them at default.

Local detail for the Lothians

• Tall Edinburgh tenement flats with high ceilings and single glazing often have undersized radiators that were adequate before rooms were reconfigured.
• Older Lothians properties frequently still run open-vented systems with a loft tank, which behave differently from sealed systems.
• Hard-to-heat solid-wall flats benefit more from controls and zoning than from simply increasing boiler output.
• Rural properties off the gas grid may be running oil or LPG systems where flushing and inhibitor practice is the same but the appliance engineer differs.

When you need a professional

A heating engineer for the system, Gas Safe registered where the boiler is involved, and an electrician for wiring new controls.

Common questions

Why is one radiator always cold?

Usually air at the top, sludge at the bottom, a seized TRV, or a system that has never been balanced.

Do smart controls save money?

They help when heating is otherwise left on unnecessarily, and zoning helps most in larger or period properties.

Related pages

• Boiler servicing and repairs

  Annual servicing, common faults and when replacement makes more sense.

• Plumbing and leaks

  Leaks, burst pipes, overflows and the water damage that follows in flats.

• Insulation and draughtproofing

  Loft, floor and wall insulation in hard-to-treat Scottish buildings.