Why your boiler might stop working in very cold weather

Condensing boilers recycle waste heat and gases and are very efficient. Unfortunately, they can stop working in very cold weather if they are not set up or installed correctly.

Condensing boilers work on the principle of a cooler return temperature. This return temperature coming into the boiler is designed to meet the hotter exhaust flue from the boiler in the heat exchanger, when they meet the heat is extracted from the exhaust flue by the heat exchanger, this causes condensation to form on the heat exchanger; it is this by-product of condensation that is taken away by the condensate pipe. It is this pipe that can freeze and cause problems.

Most condensing boilers are set up to operate in normal local conditions. But in very cold weather, especially overnight, you might find that your boiler does not work because the condensed water has frozen as they might not have been insulated.

Solve the problem 

Fortunately the solution is quite simple and should not require professional help!

Use hot - not boiling - water and carefully pour it over the end of the pipe where it is frozen, or hold a hot water bottle or heat wrap around the condensate pipe. Once the pipe has thawed you should re-set the boiler by holding in the re-set button for 10 seconds and wait for the boiler to re-fire.

If the boiler will still not fire up, you will need to call a heating engineer.

If the boiler attempts to work and finds its condensate pipe blocked it will often be programmed to retry later and this constant re-trying can cause damage to the boiler.

If the condensed waste water has backed into the boiler or home and frozen serious damage could result, which might involve a very costly repair.

Avoid the problem

To avoid the issue you could program the heating system to operate throughout the day and night, but at a much lower temperature over night. For example, 20c through the day and during a cold spell 14c. With the boiler operating throughout the night, when temperatures are normally at their lowest, the condensate pipe will be kept clear of ice and you should avoid the freezing issue. The boiler will probably be more efficient running like this during the coldest weather as the heating system won't have to be heated from such a low temperature in the morning when the heating normally comes on.