How often should radiators be bled?

Once at the start of the heating season is normal. Needing to bleed monthly points at a leak or a failed expansion vessel.

Is a cold bottom on a radiator serious?

It means sludge has settled. The radiator can be removed and flushed, or replaced — and the wider system should be checked.

Small works

A radiator that will not heat

Cold at the top, cold at the bottom — they mean different things

The short answer

Cold at the top usually means trapped air and bleeding fixes it in minutes. Cold at the bottom means sludge and the radiator needs flushing or replacing. Cold all over usually means a stuck valve pin or a system that has never been balanced. All three are small jobs; a system-wide problem is not.

What the work involves

Bleeding the radiator, freeing or replacing the thermostatic valve head and pin, balancing the lockshield valves across the property, and topping up system pressure afterwards.

Rules and responsibilities in Scotland

No certification is needed to bleed or change a radiator valve. Anything involving the boiler itself, or a gas appliance, must be done by a Gas Safe registered engineer.

What commonly goes wrong

Bleeding every radiator repeatedly without asking why air keeps appearing — regular air usually means a leak or a failed expansion vessel.

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.

Bleeding and balancing is normally under an hour for the whole property.
A thermostatic valve replacement is a low-cost part plus a short visit.
A power flush is a full-day job and an order of magnitude more.

What to do, in order

1Feel each radiator top and bottom and note which are cold where.
2Bleed the cold-at-the-top ones and re-check the boiler pressure.
3Free any stuck valve pins.
4Have the system balanced if far rooms never warm.
5If air returns within weeks, get the system investigated.

Local detail for the Lothians

Tall Edinburgh tenement flats with high ceilings often have undersized radiators rather than faulty ones.
Top-floor flats need more bleeding because air collects at the highest point of the system.
Cold-room complaints in stone-built properties are often draughts, not heating faults.

Read the Edinburgh page for a radiator that will not heat

When you need a professional

Anything at the boiler, the gas supply or the flue is Gas Safe work only.

Common questions

How often should radiators be bled?: Once at the start of the heating season is normal. Needing to bleed monthly points at a leak or a failed expansion vessel.
Is a cold bottom on a radiator serious?: It means sludge has settled. The radiator can be removed and flushed, or replaced — and the wider system should be checked.

Lothian Property is a property information and professional-introduction service operated by Maybury Scotland Limited. Lothian Property is not an estate agency. Where requested, we may connect homeowners with independent estate agents and other property professionals. How we work.

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Bathroom and kitchen extractor fans
Replacing or upgrading extraction so condensation and mould stop coming back.
Leaking taps and running toilets
A drip or a running cistern is a small job that quietly adds to a metered water bill and stains the fittings.

Last reviewed 5 September 2026.