The most common boiler breakdowns trace back to a handful of components — PCBs, fan motors, circulation pumps, gas valves, and diverter valves account for the majority of repair callouts every heating season. We stock genuine OEM replacements and quality-tested compatible parts for every major UK boiler brand.
Is your boiler showing a fault code? Use our fault code guides to identify the failing component, then order the right part here.
Part Types: What We Stock
PCBs — Printed Circuit Boards
The PCB is the boiler’s brain. When it fails, the boiler typically shuts down completely, shows a persistent fault code, or behaves erratically — igniting then cutting out, running the pump with no heat output, or failing to respond to thermostat signals.
PCB failure is among the most expensive boiler repairs. OEM PCBs carry the manufacturer’s full warranty and are designed to exact electrical tolerances. We stock original PCBs for Worcester Bosch Greenstar, Vaillant ecoTEC, Ideal Logic, Baxi 600/800 series, Glow-worm Ultimate, and Potterton Promax.
Related fault codes:
- Worcester Bosch EA (ignition fault, can indicate PCB)
- Baxi E168 (PCB fault — direct PCB failure indicator)
- Ideal L2 (fan/PCB circuit fault)
- Vaillant F28 (ignition failure, sometimes PCB-related)
Before replacing a PCB, confirm the fault is not upstream — a wiring fault, failed ignition lead, or failed gas valve can produce identical fault codes. If in doubt, call our parts helpline before ordering: 0330 124 5678.
Fan Motors
The boiler fan runs before ignition to purge the heat exchanger of any residual gas from a previous cycle, and continues running throughout the burn cycle to exhaust combustion gases through the flue. When the fan fails, the boiler cannot safely ignite and will lock out.
Fan failure symptoms: fan noise before lockout, no fan noise at all, fault codes indicating fan speed or air pressure sensor issues.
Related fault codes:
- Worcester Bosch C6, CE (fan fault)
- Glow-worm F9 (fan fault)
- Ideal L2 (can indicate fan as well as PCB)
Fan motors are brand and model specific. Always confirm the model number of your boiler before ordering — we’ll help you cross-reference if needed.
Circulation Pumps
The circulation pump moves hot water from the heat exchanger around the heating circuit. A failed pump means heat cannot reach radiators. Pump failure is sometimes misdiagnosed as a boiler fault — if the boiler fires but radiators remain cold, the pump is the first thing to check.
Pump replacement is technically possible for a competent DIYer with proper isolation, though many homeowners opt for an engineer given the risk of water damage if joints are compromised.
Vaillant F75 note: The F75 fault code on Vaillant ecoTEC boilers is triggered by the pressure differential switch, which monitors the pressure drop across the pump. A genuine F75 fault often indicates either a failed pump or a blocked pump. We stock both the pump assembly and the pressure switch separately.
Gas Valves
The gas valve controls the flow of gas from the supply to the burner. Gas valve replacement must be carried out by a Gas Safe registered engineer — this is non-negotiable regardless of competence or experience.
Signs of gas valve failure: boiler fires briefly then cuts out, fault codes indicating flame failure, gas valve opens but no ignition (often confused with ignition component faults).
Important: Before replacing a gas valve, confirm the gas supply pressure is correct and the gas meter is operating normally.
Heat Exchangers
The heat exchanger transfers heat from the burner flame to the water in the primary circuit. They fail through scale buildup (in hard water areas), physical cracking, or corrosion from an unprotected system.
Heat exchanger replacement is a significant labour job — typically 2–4 hours for an engineer depending on the boiler model. We stock OEM heat exchangers for major brands.
Prevention note: A Fernox or Magnaclean system filter dramatically extends heat exchanger life by capturing metallic debris before it can abrade internal surfaces. We stock both.
Ignition Electrodes and Leads
The ignition electrode strikes the spark that lights the burner gas. Ignition leads carry the high-voltage signal from the PCB to the electrode. Both are wear items and should be inspected at every annual service.
Symptoms of ignition failure: boiler attempts to ignite (fan runs, you may hear clicking) but fails, then locks out with an ignition fault code.
Related fault codes:
- Worcester Bosch EA (ignition lockout)
- Ideal F2 (ignition failure)
- Baxi E1 (ignition failure)
- Vaillant F28 (ignition failure)
- Glow-worm F1 (flame failure — can be ignition related)
Diverter Valves
Diverter valves are found in combi boilers. They switch the flow of heated water between the central heating circuit and the domestic hot water heat exchanger. A stuck or failed diverter valve typically presents as either no hot water (valve stuck in heating position) or no heating (valve stuck in hot water position).
Diverter valve repair is often possible before full replacement — the valve actuator motor is sometimes the failing component rather than the valve body itself. Call our helpline to discuss before ordering.
Pressure Switches
The pressure switch monitors flue gas pressure (or water pressure, depending on type). Failure prevents safe ignition. The Vaillant F75 fault is almost always traced to the pressure differential switch monitoring pump operation.
Burners
Burners require replacement when they become cracked, blocked with debris, or suffer surface corrosion from condensate contamination in condensing boilers. Burner replacement must be carried out by a Gas Safe engineer.
OEM vs Compatible Parts
Original Equipment Manufacturer (OEM): Parts manufactured to the exact specification of the boiler manufacturer. Carry the manufacturer’s full warranty. Recommended where the boiler is under manufacturer warranty, or where the customer specifies OEM.
Compatible (non-OEM): Manufactured to an equivalent specification by third parties. Quality varies significantly between suppliers — we only stock compatible parts from suppliers we’ve tested and verified. Typically 15–40% lower price than OEM equivalents.
All products on our site are clearly labelled OEM or Compatible. If you’re unsure which to specify for a particular job, our helpline can advise.
Need This Part Fitted?
Gas components (gas valves, PCBs connected to gas circuits, burners) must be fitted by a Gas Safe registered engineer. Attempting to work on gas components without Gas Safe registration is illegal and can be dangerous.
If you’ve sourced your part through us and need a trusted engineer to install it, we work with a network of recommended heating specialists across the UK.
Call 0330 124 5678 to discuss your requirements or to confirm part compatibility before ordering.