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PUMPS & MOTORISED VALVES

Pipes Hot but Radiators Cold

Hot pipes with cold radiators usually point to closed or stuck valves, poor balancing, blocked radiator tails, sludge or insufficient flow through the emitters.

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Isolate electrical power before opening pumps, actuators or wiring centres

Heating pumps and motorised valves may contain mains voltage and hot water. Stop if a pump is seized, very hot, leaking or if a valve actuator is buzzing continuously.

MOST LIKELY CAUSES

Start with these

TRVs or lockshields closed Hot water reaches the branch but not the radiator.
Stuck TRV pins The valve may remain shut internally.
Poor balancing Flow may bypass or favour other radiators.
Blocked radiator or tail Sludge can stop water entering the panel.
◫ Symptom variations Match the exact circulation or zone pattern. ⌄
  • Pipe hot up to valve
  • Radiator panel cold
  • One side hot and one side cold
  • Heat improves when other radiators are closed
  • Several older radiators affected
✓ Quick checks Simple checks before removing covers. ⌄
  1. Confirm a heating demand exists.
  2. Check whether one zone or the whole system is affected.
  3. Listen for pump or actuator operation.
  4. Check system pressure and trapped air.
  5. Do not force seized valves or hot pumps.
1 Step 1 — Check both radiator valves Isolate power before removing covers or touching wiring. ⌄

Open the TRV and lockshield enough for flow.

2 Step 2 — Compare nearby radiators Isolate power before removing covers or touching wiring. ⌄

See whether the problem is local or widespread.

3 Step 3 — Bleed and rebalance Isolate power before removing covers or touching wiring. ⌄

Remove air and adjust flow through competing radiators.

⌁ Common causes explained Why pumps and zone valves fail. ⌄

Hot pipes with cold radiators usually point to closed or stuck valves, poor balancing, blocked radiator tails, sludge or insufficient flow through the emitters.

⌘ Advanced diagnostics Heating-engineer checks and repair work. ⌄
  • Check TRV pin movement.
  • Inspect valve internals.
  • Flush radiator and tails.
  • Measure flow and return temperatures.
  • Check differential pressure.
▣ Parts that may need replacing Common components linked to this fault. ⌄
  • TRV
  • Lockshield valve
  • Radiator tail
  • Radiator
  • Circulation pump
! When to call a heating engineer Conditions that should end basic troubleshooting. ⌄
  • The pump or actuator contains mains wiring.
  • The pump is seized, leaking or overheating.
  • A valve body is stuck.
  • One or more zones remain uncontrollable.
  • Internal testing is required.
? Frequently asked questions Common pump and valve questions. ⌄

Can I force a motorised valve open?

Use only the normal manual lever as described by the manufacturer. Do not force a seized valve body.

Why is a heating pump hot?

Some warmth is normal, but excessive heat with no circulation may indicate a seized rotor or failed motor.