Frozen Condensate Pipe on Your Boiler & How To Defrost

Nothing ruins a freezing cold December morning faster than your boiler locking out with no heating or hot water.

When it drops below -0 degrees Celsius, if your boiler is flashing an error code like EA 227 (Worcester Bosch) E28 (Intergas), F28/F29 (Vaillant), E01 (Keston), F1 (Glow-worm), or simply refusing to fire up on a frosty day, the most likely culprit is a frozen condensate pipe.

This is the single most common winter boiler fault in the UK – especially on condensing combi boilers fitted since 2005. The good news? In almost every case you can fix it yourself in under 10 minutes with no tools and no engineer call-out.

What Is a Condensate Pipe and Why Does It Freeze?

Modern gas boilers are condensing appliances – they extract extra heat from the flue gases, turning water vapour into liquid (condensate). This harmless acidic water drains away through a small white plastic pipe, usually 22 mm or 32 mm, that runs from the boiler to an outside drain or soakaway.

In freezing weather the condensate can turn to ice inside the pipe, especially where it runs outside or through an unheated garage. Once blocked, the boiler detects the backup and shuts down safely.

Step-by-Step: How to Thaw a Frozen Condensate Pipe Yourself

1. Locate the pipe – Look for a white plastic pipe (usually 22 mm or 32 mm) coming out of the bottom or side of the boiler and running to an outside drain, gutter or soakaway.
2. Find the frozen section –  The blockage is almost always the external part that’s exposed to the cold.
3. Thaw it safely
   • Pour warm (not boiling) water from a jug or kettle slowly over the pipe, starting at the highest point and working downwards.
   • Repeat until you hear water flowing freely inside the pipe.
   • If the pipe is very long, use a hot-water bottle or hairdryer on a low setting (never use a naked flame).
4. Reset the boiler – Once the pipe is clear, press and hold the reset button (usually the spanner symbol) for 5 seconds. The boiler should fire up straight away.
5. Check it’s working – Turn on a hot tap or heating – you should see water flowing out of the external pipe end (a steady trickle).

How to Stop The Condensate Pipe Freezing Again

• Upgrade to 32 mm pipe The larger diameter is much less likely to freeze. Most engineers fit 32 mm from the boiler to the first external joint.
• Insulate the external section Use foam pipe lagging (available at any DIY store) or a dedicated condensate pipe insulation kit.
• Fit trace heating A low-wattage electric heating cable wrapped around the pipe (around £40–£80) keeps it above freezing.
• Shorten the external run If possible, reroute the pipe so less of it is outside.
• Fit a condensate pump For boilers in lofts or with very long runs, a small pump pushes the water away quickly.

Which Boilers Are Most Affected Frozen Condensate Pipes?

All condensing boilers can freeze, but the worst offenders are:

• Vaillant ecoTEC Pro/Plus, ecoFIT Pure
• Worcester Bosch Greenstar i/Si/CDi/4000/8000
• Ideal Logic+/Max/Vogue
• Glow-worm Energy/Ultimate/Betacom
• Intergas HRE/ECO RF/Xtreme
• Keston C35/C40/Qudos
• Baxi Duo-tec/Platinum/EcoBlue

Boilers in lofts, garages or with long external pipe runs are particularly vulnerable.

When You Should Call a Gas Safe Engineer Instead

• The boiler still won’t fire after thawing (possible deeper blockage or other fault)
• You can’t safely reach the frozen section (high up or on a ladder)
• You’ve thawed it but the fault returns every time the temperature drops below zero

Frequently Asked Questions About Frozen Condensate Pipes

How cold does it have to be for the pipe to freeze?

Usually below -3 °C for a few hours, but even -1 °C overnight can be enough if the pipe is exposed.

Why don’t all boilers have this problem?

Older non-condensing boilers don’t produce condensate, and some newer installations already have 32 mm pipe or trace heating.

Is a frozen pipe dangerous?

No – the boiler shuts down automatically to prevent damage or carbon monoxide risk.

Will my home insurance cover a frozen pipe call-out?

Most policies don’t cover boiler breakdowns, but some home-emergency add-ons do. Check your policy wording.

How much does an engineer charge to thaw a pipe?

£90–£150 call-out, though many now offer a fixed “frozen condensate” price.

Still got no heating on a freezing day? Drop your boiler make and model in the comments and we’ll tell you the exact error code to look for and the quickest fix.

Stay warm, The Boilers2Go Team