FAULTNEST HEATING
Heating Fault-Finding Guides
Diagnose common heating problems involving radiators, boiler pressure, thermostats, pumps, valves, timers and hot water controls.
Do not open sealed boiler or gas compartments
User checks should remain outside sealed combustion areas. Gas work, combustion testing and internal boiler repairs must be completed by a suitably qualified engineer.
Read FaultNest safety guidance →BROWSE GUIDES
Choose the problem
Open the section that matches the fault, then choose the individual troubleshooting guide.
Radiator faults Cold spots, noises, leaks and poor circulation.
Radiator Cold at the Top
Bleed trapped air and check system pressure.
Radiator Cold at the Bottom
Check sludge, restricted flow and balancing.
Radiator Not Heating
Check valves, air, balancing and circulation.
One Radiator Not Working
Inspect TRV, lockshield and local pipework.
All Radiators Cold
Check boiler operation, pump and controls.
Radiator Making Noise
Identify air, flow velocity and expansion noises.
Radiator Leaking
Check valves, vents, tails and panel corrosion.
Radiators Heat Unevenly
Balance the system and inspect circulation.
Boiler pressure faults Low pressure, high pressure and repeated pressure loss.
Boiler Pressure Keeps Dropping
Check leaks, expansion vessel and pressure relief discharge.
Boiler Pressure Too Low
Repressurise safely and look for the cause.
Boiler Pressure Too High
Check filling loop, expansion vessel and overheating.
Pressure Rises When Heating Is On
Assess expansion vessel and system water expansion.
Boiler Relief Pipe Dripping
Identify PRV discharge and underlying pressure faults.
Boiler Needs Repressurising Often
Trace system leaks and expansion faults.
Thermostats and controls Timers, programmers, thermostats and smart controls.
Thermostat Not Working
Check batteries, settings, wiring and receiver communication.
Heating Won’t Turn On
Check programmer, thermostat, boiler and zone controls.
Heating Won’t Turn Off
Inspect thermostats, valves and relay faults.
Smart Thermostat Offline
Check Wi-Fi, power and receiver links.
Heating Programmer Not Working
Check clock, power, settings and outputs.
Thermostat Temperature Is Wrong
Check location, calibration and sensor faults.
Heating Comes On Randomly
Check schedules, frost protection and control faults.
Heating Not Following Schedule
Review programmes, overrides and time settings.
Pumps and motorised valves Circulation, humming, stuck valves and zone faults.
Heating Pump Not Working
Check power, seized rotor and control signals.
Heating Pump Making Noise
Identify air, wear and incorrect speed settings.
Motorised Valve Not Working
Check actuator, microswitch and valve body.
Zone Valve Stuck
Free or replace the actuator and inspect the valve.
Heating Only Works Upstairs
Check pump performance, air and balancing.
Heating Only Works Downstairs
Inspect zone valves, controls and circulation.
Boiler Runs but Radiators Stay Cold
Check pump, valves and trapped air.
Pipes Hot but Radiators Cold
Check valves, balancing and radiator restrictions.
Hot water and cylinder faults No hot water, unstable temperature and cylinder issues.
No Hot Water
Check boiler, cylinder, immersion and controls.
Hot Water Not Hot Enough
Check thermostat, mixing valve and heat source.
Hot Water Too Hot
Inspect thermostats and blending valves.
Hot Water Runs Out Quickly
Assess cylinder capacity and heating recovery.
Hot Water Cylinder Not Heating
Check zone valves, thermostats and heat source.
Immersion Heater Not Working
Check fused supply, thermostat and element.
Tundish Dripping
Understand unvented cylinder safety discharge.
Hot Water Temperature Fluctuates
Check flow, boiler modulation and mixer valves.
Boiler symptoms and warnings Noise, locking out, cycling and visible fault signs.
Boiler Keeps Turning Off
Check pressure, flow, overheating and controls.
Boiler Keeps Locking Out
Use the fault code and safe external checks.
Boiler Making Banging Noise
Recognise kettling, air and circulation faults.
Boiler Making Whistling Noise
Check scale, flow and pump issues.
Boiler Short Cycling
Assess thermostat demand, flow and oversized output.
Boiler Fan Running Constantly
Check operating state and control faults.
Boiler Condensate Pipe Frozen
Thaw the external pipe safely.
Boiler Display Blank
Check fused supply, isolation and electrical faults.
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