Top 5 Common Grant Boiler Problems and the Parts to Fix Them

Grant boilers are trusted across the UK for their reliability and performance. However, like all heating systems, they are subject to wear and faults over time. Whether you’re an engineer or a homeowner trying to resolve an issue, knowing which part to replace is key.

Below are the top five most common Grant boiler problems and the exact replacement parts to solve them.

1. Burner Motor Failure

Symptoms:

Loud humming or mechanical noise
Boiler fails to ignite
Persistent lockout

Cause:
Burner motors degrade over time, especially with constant use. Bearings can seize or the motor may fail electrically.

Potential Solution:
Replace with a Grant Burner Motor – Part No. 19009720

2. Pressure Relief Valve (PRV) Leaking

Symptoms:

System pressure dropping
Discharge pipe dripping
Boiler needs regular repressurising

Cause:
The PRV may become worn or fail to seal properly after frequent pressure fluctuations or overpressure events.

Potential Solution:
Install a new Grant Pressure Relief Valve PRV 3bar MPCBS50 MPCBS124

3. Photocell Failure (Lockout Issues)

Symptoms:

Lockout light illuminates
Boiler attempts ignition but fails
Starts and stops intermittently

Cause:
A dirty or faulty photocell can fail to detect the flame, causing the boiler to shut down as a safety precaution.

Potential Solution:
Replace with the Riello Analogue Photodiode RDB Photocell 20193432

4. Fuel Pump Not Delivering Oil

Symptoms:

Boiler fails to fire
Motor runs but no combustion
No fuel reaching the burner

Cause:
The oil pump may suffer internal wear or lose pressure, particularly in older models or poorly maintained systems.

Potential Solution:
Fit a Danfoss Fuel Pump BFP11L3 Diamond 071N7141

5. No Hot Water or Intermittent Heating

Symptoms:

Hot water stops suddenly
Radiators heat but hot taps do not
Boiler doesn’t respond to demand

Cause:
Failure of the DHW sensor or diverter valve may prevent proper water flow or temperature detection.

Potential Solution:
Check and replace the Grant Sensor Probe Direct H/W MPCBS98 PCB Vortex Pro Combi or Grant Divertor Valve MPCBS20A Combi

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Published on 06 May 2025