Glow Worm Boiler Repairs London

Glow-worm Boiler Repair Help Centre

Common Glow-worm faults, fault codes, safe checks, and when to call a Gas Safe engineer.

We specialise in Glow-worm boiler repairs across London.

Gas Safe registered engineers for safe diagnosis, repair and testing.

24/7 availability with London wide call handling and booking.

Jump to: Fault Codes · F75 Fault · Pressure · Frozen Condensate · Repair or Replace

Quick Checks Before You Call Anyone

These take 60 seconds and solve a surprising number of lockouts:

1. Check the pressure gauge: If below 1 bar, top up (see guide below). More detail in our complete pressure guide.
2. Note the fault code: Glow-worm displays show F codes like F28, F75, F22. Write it down before calling.
3. Check your fuse box: Boilers need electricity, a tripped switch is an easy fix.
4. Check thermostat and timer: Settings can change after clock changes or dead batteries.
5. Freezing weather? The condensate pipe may be frozen (see winter section below).
6. Reset once only: Press the reset button on the front panel once, wait 60 seconds. If it locks out again, stop and call an engineer.

Glow-worm Fault Codes

Note: Glow-worm is part of the Vaillant Group, so many fault codes are similar to Vaillant. If unsure, call us and we will help you identify your specific code.

F28: Ignition Failure

What is happening: The boiler is trying to ignite but cannot establish a flame after multiple attempts.

Common causes: Frozen condensate pipe (winter), gas supply interruption, faulty ignition electrode, blocked or damaged flue, gas valve fault.

What to try: Check if your gas hob or other gas appliances work. In freezing weather, check the condensate pipe for ice. If gas supply is fine but the boiler will not ignite, call an engineer.

F75: Pump or Pressure Sensor Fault

What is happening: The boiler cannot detect a pressure change when the pump runs. This is one of the most common Glow-worm faults and is shared across platforms.

Common causes: Often linked to pump performance, pressure sensor issues, air or debris in the hydraulic block, or system conditions. Hard water and older systems can contribute to debris and restriction over time.

What to try: Check the pressure gauge first. If pressure is below 1 bar, top up and reset. If pressure is fine but F75 persists, the pump or sensor likely needs attention. Call an engineer.

Note: F75 is common on older Glow-worm models. It often requires pump replacement or sensor cleaning rather than just a reset.

F22: Low Water Pressure

What is happening: System pressure has dropped below the minimum operating level.

Common causes: Small leak in the system, recently bled radiators, pressure relief valve discharge, expansion vessel needs recharging.

What to try: Top up pressure using the filling loop (see below). If pressure drops again within days, there may be a leak. Read our pressure guide for step by step instructions.

How to Top Up Pressure (Glow-worm)

If you are not comfortable using the filling loop, stop and call a Gas Safe engineer.

Do not remove the boiler casing. If you cannot locate the filling loop easily, call an engineer.

1. Locate the filling loop (usually underneath the boiler, a braided silver hose with one or two valves).
2. Ensure the boiler is off and cool.
3. Open the valves slowly, a quarter turn at a time.
4. Watch the pressure gauge rise to between 1.0 and 1.5 bar.
5. Close both valves fully.
6. Switch the boiler back on.

Do not exceed 2.0 bar. If you overfill, stop and call an engineer.

If you need to top up frequently (more than once a month), there is likely a leak. Call us for a diagnosis.

Frozen Condensate Pipe (Winter)

In freezing weather, a frozen condensate pipe is one of the most common causes behind F28 and F29 lockouts on Glow-worm boilers. This is often safe to resolve with the steps below. If you are unsure, or the boiler will not restart, call an engineer.

Signs: Boiler locked out with F28 or F29, freezing temperatures outside, gurgling sound when boiler tries to start.

What to do:

1. Locate the condensate pipe (white or grey plastic pipe exiting to an outside drain).
2. Pour warm water (not boiling) over the frozen section.
3. Reset the boiler once thawed.

Full instructions: Frozen condensate pipe guide.

If it keeps happening, we can reroute the pipe internally or add insulation to reduce future freezing.

Why These Faults Are Common in London Homes

Hard water, older pipework, and winter weather make certain faults more likely in London properties:

• F75 (pump and sensor): London’s hard water can contribute to debris build up over time, affecting pump performance and triggering F75 faults.
• Frozen condensate pipes: External pipes exposed to freezing temperatures are a common cause of F28 and F29 faults in winter.
• Pressure fluctuations: Older London properties with microbore pipework or poorly balanced systems can see more F22 low pressure faults.
• Sludge accumulation: Hard water areas accumulate more magnetite sludge over time, restricting circulation and contributing to pump and sensor faults.

Glow-worm Models We Repair

We repair all Glow-worm gas boiler models including:

• Energy: Current combi range
• Easicom: Popular mid range combi (now discontinued but widely installed)
• Betacom: Older combi range, parts often still available
• Flexicom: System and combi models
• Ultimate: Higher specification models

We carry common Glow-worm parts and can source others quickly. As part of the Vaillant Group, many parts are shared across platforms.

Repair or Replace?

Glow-worm boilers typically last 10 to 15 years with proper maintenance. If yours is approaching that age and needs a major repair (heat exchanger, PCB, pump), replacement may be more cost effective.

We give honest advice either way. Read more: Repair or replace? An engineer’s guide.

If you decide on a new boiler: New boiler installation.

Glow-worm Servicing

Annual servicing keeps your Glow-worm running efficiently and helps maintain warranty terms. We service Glow-worm models and provide a clear report after each visit.

We recommend servicing in late summer or early autumn, before the heating season. Book your boiler service.

Renting? Landlords: Check This

Tenants: Your landlord is usually responsible for boiler repairs. Contact them first and keep written records, especially if you have no heating or hot water.

Landlords: Stay compliant with our Gas Safety Certificate (CP12) service. See our full London landlord checklist covering gas safety, EPCs, and maintenance requirements.

London Wide Coverage

We repair Glow-worm boilers across all London boroughs. See our London coverage area or find your local page:

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