The oil pump on a domestic boiler (typically a Danfoss BFP or Suntec) lifts oil from the tank, raises pressure to 7-14 bar and feeds it to the nozzle, where it atomises into the combustion chamber. When the pump fails or weakens, the boiler either won’t fire, fires poorly, or makes strange noises.
Here’s how to diagnose the specific symptoms, what a replacement costs (£140-£220 fitted), and when it’s the pump vs something else that looks like a pump problem.
Symptom 1: boiler motor runs but no ignition
What you see: you hear the motor spin up. Lockout light comes on after 10-30 seconds. Combustion never starts.
Likely cause: pump isn’t building enough pressure to open the nozzle. Could be:
- Air locked in the pump
- Dirty pump suction filter
- Failing pump rotor (worn internal vanes)
- Oil filter before the pump is clogged
Fix: start by checking the oil filter outside (on the pipe from the tank). If it’s clogged (dirty, sooty), replace. £25-£50 part. If the filter is clean, service the pump. If the pump itself is worn, replace.
Symptom 2: pump whining or loud humming
What you see: distinct whining or grinding noise from the burner when running, often louder than the motor.
Likely cause: pump bearings failing, or pump is cavitating (running partly dry because of air or a blocked suction line).
Fix: check oil level (tank might be near empty, pulling air). If tank is fine, it’s a worn pump. Replace.
Cavitating pumps run hot and fail completely within weeks. Don’t ignore the noise.
Symptom 3: oil leaking from the pump body
What you see: oil drips visible around the pump or below it. Fuel smell.
Likely cause: pump seal failure, usually from age (15+ years) or over-pressure.
Fix: STOP using the boiler immediately. Leaking oil under pressure is a fire risk. Call us. See Emergency Plumbing.
Replacement pump with new seals fitted is £140-£220. Cleanup of spilled oil may add £50-£150 if there’s contamination of the boiler housing.
Symptom 4: pressure too high or too low at nozzle
What you see: smoky combustion, soot in the flue, yellow flame, fault lockouts within 20 seconds of firing.
Likely cause: pump pressure out of spec. Could be:
- Pump pressure regulator stuck (cheap fix if adjustable)
- Pump vanes worn
- Wrong pump fitted (very rare)
Fix: combustion analyser check first (this needs an engineer). If pressure is recoverable with adjustment, £85-£140 labour. If pump is worn, replace £140-£220.
Symptom 5: pump won’t prime after oil delivery
What you see: tank was refilled after running empty. Boiler won’t restart. Lockout every attempt.
Likely cause: air in the oil line that the pump can’t clear on its own. Modern pumps self-bleed on 2-3 reset cycles. Older ones (10+ years) often don’t.
Fix: manual pump bleeding. £75-£120 for an engineer visit, or DIY if you have a spanner and know the pump bleed screw location (2-3mm Allen key on most Danfoss BFPs, on the pump casing opposite the pressure gauge port).
DON’T keep pressing the reset button on an un-primed pump. This floods the combustion chamber.
Symptom 6: intermittent firing
What you see: boiler fires, runs 2-5 minutes, locks out. Restart works briefly, locks out again.
Likely cause: pump is starting okay but can’t sustain pressure under load. Often due to worn internal vanes, a partially collapsed oil line (kinked or buried in insulation), or a failing photocell.
Fix: diagnose by process of elimination. Pump test with an external pressure gauge first. If pump holds pressure in a bench test, look at the oil line or photocell. If pump drops under load, replace.
Replacement cost in Belfast (2026)
| Pump scenario | Typical total |
|---|---|
| Danfoss BFP pump replacement | £140-£200 |
| Suntec pump replacement | £160-£220 |
| Pump + new oil line + new nozzle | £180-£280 |
| Pump replacement during annual service | £95-£150 (service discount) |
All prices include labour, commissioning and OFTEC record.
When it’s NOT the pump
Symptoms that look like pump issues but usually aren’t:
- Won’t fire when cold but fires when warm: photocell issue, not pump
- Locks out in wet weather: condensate or flue issue, not pump
- Runs then dies 30 min later: thermostat or overheat safety, not pump
- Random lockouts with no pattern: control box, not pump
If you’re not sure, a diagnostic visit (£75-£120) with an engineer confirms the cause before you commit to a pump replacement.
Pump lifespan
Typical pump lasts 12-20 years on a well-serviced boiler. On a boiler that’s been neglected (missed services, contaminated oil, frequent lockouts), 6-10 years.
If the boiler itself is 15+ years old and the pump is failing, the honest conversation is about boiler replacement not pump replacement. See When should I replace my boiler.
Prevention
- Annual oil boiler service (catches pump wear early)
- Clean oil: buy from reputable suppliers, avoid end-of-tank dregs
- Keep the external oil filter changed (every service, without exception)
- Don’t let the tank run empty (airlocks wear the pump faster than anything)
- Don’t reset the boiler repeatedly through lockouts (floods the chamber, stresses the pump)
Book a repair or diagnostic visit
Send us the boiler make and model, the symptom pattern, and any fault code or lockout light. We’ll tell you if it sounds like a pump or something else, and book a slot.
Related services: Oil Boiler Servicing · Boiler Repair · Emergency Plumbing
Related guides: Oil boiler not firing up · Oil boiler fault codes · Common oil boiler problems · When should I replace my boiler