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A Glow-worm boiler that won't fire up and doesn't show a fault code can be difficult to diagnose. Most modern boilers display an error code when something goes wrong, but some faults happen without triggering one.

Start with a few basic checks. If nothing obvious is wrong, the fault is usually hidden inside the boiler and needs professional diagnosis.

Glowworm-Boiler-Not-Working-No-Fault-Code
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What Does It Mean When There's No Fault Code?

Fault codes help identify specific boiler problems such as low pressure, ignition failure or flame loss. Common examples include:.

  • F22 — Low system pressure
  • F28 — Ignition failure
  • F29 — Flame loss

When no code appears, the boiler can still have a fault. It simply means the control board hasn't identified a condition that generates an error message. If your boiler later starts displaying an error, see our complete guide to Glow-worm boiler fault codes for model-specific explanations.

If your boiler has stopped working completely, a professional inspection is normally the quickest way to identify the cause.

Common Signs Your Glow-worm Boiler Isn't Working

Typical symptoms include:

  • Boiler won't ignite
  • No heating
  • No hot water
  • Boiler appears to have power but does nothing
  • Normal pressure but no operation
  • Intermittent heating or hot water

Checks You Can Do Before Calling an Engineer

Before arranging a repair, check the basics.

Check the gas supply

  • Make sure the gas supply is on.
  • Check the isolation valve hasn't been turned off.

Check the boiler pressure

  • Pressure should usually be around 1.5 bar when cold.
  • Top up the pressure if required using the filling loop.
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Check the power supply

  • Check the fused spur.
  • Check the consumer unit for a tripped breaker.

Reset the boiler

Follow the instructions in your Glow-worm manual. A reset may clear a temporary control issue.

Why a Glow-worm Boiler Stops Working Without a Fault Code

Glow-worm Boiler Stops Working Without a Fault Code

Several faults can prevent the boiler from operating without generating an error.

Blocked plate heat exchanger

Limescale or sludge can restrict water flow, reducing efficiency or preventing normal operation.

Faulty diverter valve

A seized or failed diverter valve may stop heating or hot water from working even though the boiler appears normal.

Temperature sensor problems

Incorrect sensor readings can cause the boiler to shut down as a safety precaution without displaying a fault.

Flow switch or microswitch faults

These switches tell the boiler when there is demand for heating or hot water. If they fail, the boiler may never begin its firing sequence.

Frozen condensate pipe

During freezing weather, the condensate pipe can ice over and stop the boiler operating.

Safe Steps You Can Try

Some simple checks may restore operation.

  • Repressurise the boiler if pressure is low.
  • Bleed radiators if trapped air is affecting circulation.
  • Carefully thaw a frozen condensate pipe using warm (not boiling) water.
  • Confirm the boiler has both gas and electrical supply.

Avoid removing the boiler casing or attempting repairs yourself.

When You Need a Gas Safe Engineer

Call an engineer if:

  • The boiler still won't start.
  • Heating and hot water remain unavailable.
  • You suspect an internal component has failed.
  • You smell gas or suspect a gas leak.

Internal components should only be repaired by a Gas Safe registered engineer. If these checks don't restore heating or hot water, arrange a professional boiler repair in London before the fault becomes worse.

What Affects Repair Cost?

Repair cost depends on the underlying fault, labour time and whether replacement parts are required.

  • A simple fault may need diagnosis and a minor repair, while component failures can require more involved work.
  • A quotation should only be confirmed once the boiler has been professionally diagnosed.

Do not assume a fixed repair cost from the symptoms alone.

Should You Repair or Replace the Boiler?

If your Glow-worm boiler regularly breaks down or repair costs continue to increase, replacing it may become the more economical option.

Age, reliability and repair history should all be considered before making a decision.

Need Help With a Glow-worm Boiler?

If your Glow-worm boiler isn't working and there's no fault code, Serviceteam's Gas Safe engineers can identify the fault and recommend the most cost-effective repair.

Book an appointment online or contact us for expert boiler repairs across London.

Get lightning fast quotes. Alternatively, we do offer site surveys where needed.