Boiler hot but radiators cold: pump, valve and airlock diagnosis
If the boiler body gets hot but nothing reaches the radiators, the heat has nowhere to go. That is a circulation failure, and it usually costs far less to fix than people fear.
How we read hot boiler with cold radiators on site
A seized pump is silent or humming without flow. A failed motorised valve leaves one zone dead while the other works. An airlock in a high pipe run gives intermittent behaviour that changes when you bleed. Heavy sludge produces sluggish, uneven warmth across the whole house rather than a single dead zone. The pattern of which radiators are cold tells an engineer which of the four it is.
Detail that affects your quote for hot boiler with cold radiators
- One dead zone, one working zone points at a motorised valve
- All radiators cold points at the pump or a closed system valve
- Top-floor only cold suggests air rather than sludge
- Cold at the bottom of individual radiators means sludge
- Pumps often free off temporarily then fail again within days
Published business details
- Based at 24 Bristol Road, Radstock, BA3 3EE
- Telephone enquiries: 07516 118198
- Opening hours: Monday to Friday, 8:30am to 5:00pm
Questions we get asked
- Should I bleed the radiators first?
- Bleeding is safe and worth doing, but re-check system pressure afterwards and top up if it has dropped.
- Is a new pump a big job?
- It is normally a same-visit replacement where isolation valves are fitted either side.
Where we deal with this
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Services that cover this
Sorted quickly: hot boiler with cold radiators
The honest position: Map which radiators are cold before calling. That map is the diagnosis, and it usually ends at a pump or valve.
For gas work, use a Gas Safe registered engineer; for oil work, use an OFTEC-registered technician.
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