Pump not running · S-Plan · Needs a proper trace
Circulating pump seized
“The boiler fires, makes a terrible kettling noise, then cuts out. The radiators hardly get warm.”
In short
The boiler fires but the water is not being circulated. The pump has 230 V across L-N but does not run: seized. The boiler overheats and locks out.
What the customer says
- “The boiler fires, makes a terrible kettling noise, then cuts out. The radiators hardly get warm.”
- “Boiler fires up, bangs and kettles, then cuts out. Rads are barely warm.”
The controls and boiler are doing their job. Look only at the pump and its supply.
How to find it in the simulator
If this is your home: this page is written for heating engineers. Mains wiring and gas appliances are not DIY jobs; call a Gas Safe registered engineer. If you smell gas, leave the building and call the National Gas Emergency Service on 0800 111 999.
In the simulator the meter is safe. On a real system: isolate and prove dead before you touch a terminal, and make live tests only if you are trained and equipped for them. The steps below are the method as practised in the simulator, in its own words, for competent persons and for learners under the supervision of one.
- 01
CONFIRM the complaint yourself: spur ON, run the simulation, ask for heating only, then hot water only. Watch the valve(s), boiler and pump.
- 02
Heat is being made but not moved. Is the pump running while the boiler fires?
- 03
Meter the pump: L to its own N. 230 V and not turning = seized pump.
- 04
No supply at the pump? Follow it back to the boiler's pump-live terminal.
- 05
The fault lies between the LAST point with 230 V and the FIRST without.
- 06
ISOLATE (stop the simulation) before you touch anything. Continuity only on a dead circuit.
- 07
Click Report Fault, then the wire or part you have PROVEN faulty.
What the meter shows
Where to probeWhile the boiler fires, meter the pump's L to the pump's own N.
The readingYou are looking for a part that HAS its supply (230 V, and a good neutral) and still does not operate. That part has failed.
The faultThe pump has 230 V across L-N but does not run: seized. The boiler overheats and locks out.
Common wrong guesses
Boiler fires but overheats quickly and radiators stay cool. What do you check first?
- Room stat setting
- Programmer clock
Show the right answer
Whether the pump is actually running
Heat is being made but not moved: circulation.
Related
More pump not running faults
Components involved
The system
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