What to do if your boiler’s condense pipe has frozen

It’s freezing outside.  You turn on the heating ….

…and nothing happens.

Your heart sinks as you prepare to try to find a gas heating engineer who is able to come out and deal with your emergency.

Your boiler might also be showing a fault code (e.g. Vaillant F28/F29, Ideal L2 and Worcester a Blue Flashing Light).

But quite a few boiler breakdowns in icy weather turn out to be caused by nothing more than a frozen condense pipe. 

About boiler condense pipes

All modern, high efficiency boilers are fitted with a waste pipe which disposes of the additional condensation that results from exhaust gases. Such boilers cannot run without a condensate pipe. These newer types of boiler are 10-12% more efficient than the older gas boiler models. 

What should you do if your condenser pipe is frozen?

If there was no other sensible and cost-effective option except routing the pipe to the outside of your home when the boiler was fitted, you are likely to encounter this problem sooner or later.

Here are some preventative solutions:

1. Ideally, the pipe should be lagged as far as possible, if it this wasn’t done on installation. Try attaching suitable water-proof and weather-proof insulation over the outside of the pipe to prevent re-freezing. “Class O” pipe insulation is suitable for external use and should be available from DIY outlets and plumbing/heating suppliers.
2. As a temporary measure only during very cold weather run the heating system with the boiler thermostat (as distinct from the room thermostat) set to maximum.
3. If you do have to unfreeze the condense pipe you should not attempt to thaw it if you cannot easily reach it from ground level.  
4. To thaw, assuming you can do it safely, you can apply a hot water bottle, a microwaveable heating pack (the sort used for muscular aches and pains) or cloths soaked in warm water to the exterior of the pipe, close to the likely point of blockage. Do NOT use boiling water, which can crack pipes, or melt certain types of plastic. 
5. Once the blockage has been thawed and cleared, consult the boiler operating instructions or check the manufacturer’s website for guidance on any action needed to “reset” the fault code/alarm and start the boiler.

IMPORTANT: If in doubt about how to unfreeze the pipe or do not feel comfortable doing so, or you feel it is not safe for you to attempt it, make sure you call a Gas safe engineer.

Should the boiler fail to start up after this then consult your gas-safe engineer to investigate further.