Frozen condensate – don’t get caught out this winter!

The UK is currently experiencing prolonged spells of extremely cold weather.

This can result in a significant increase in the number of calls to boiler manufacturers and heating installers from householders with condensing boilers where the condensate drainage pipes have frozen, causing the boiler to temporarily shut down.

In the vast majority of cases, this occurs when part of the condensate drainage pipe is located externally.

In order to minimise the risk of freezing during cold spells, the following methods of installing condensate drainage pipe should be used, in order of priority:

Step 1

Wherever possible, the condensate drainage pipe should be routed and terminated so that the condensate drains away from the boiler under gravity to a suitable internal foul water discharge point such as an internal soil and vent stack, internal kitchen, bathroom or washing machine waste pipe or similar.

A suitable permanent connection to the foul waste pipe should be used and all other relevant guidance in British Standards and/or the boiler manufacturer’s instructions should be followed.

Please note, where a new or replacement boiler is being installed, access to an internal “gravity discharge” point should be one of the factors considered in determining boiler location, alongside flue position, convenience of supply and system pipe runs etc.

Step 2

Where “gravity discharge” to an internal termination is not physically possible, or where very long internal runs of drainage pipe would be required to reach a suitable discharge point, condensate should be removed using a proprietary condensate pump, of a specification recommended by the boiler or condensate pump manufacturer.

The pump outlet pipe should discharge to a suitable internal foul water discharge point such as an internal soil and vent stack, internal kitchen, bathroom or washing machine waste pipe.

A suitable permanent connection to the foul waste pipe should be used and all other relevant guidance in British Standards and/or the boiler and condensate pump manufacturers’ instructions should be followed.

Step 3

If no other discharge method is possible then the use of an externally run condensate drainage pipe terminating at a suitable foul water discharge point, or purpose designed soakaway, may be considered

If this method is chosen then the following measures should be taken:

• The pipe should be run internally as far as possible before going externally and the pipe diameter should be increased to 32mmm, marked A on the diagram, before it passes through the wall to the exterior. The pipe should be insulated using suitable waterproof and weather resistant insulation

• The external pipe should take the shortest and least exposed route to the discharge point, and should “fall” as steeply as possible away from the boiler, with no horizontal runs in which condensate might stand

• The use of fittings, elbows etc. should be kept to a minimum and any internal “burrs” on cut pipework should be removed so that the internal pipe section is as smooth as possible

• Where the pipe terminates over an open drain or gully, the pipe should terminate below the grating level, but above water level, in order to minimise “wind chill” at the open end. The use of an additional drain cover may offer further protection

• In situations where there are likely to be extremes of temperature or exposure, the use of a proprietary trace-heating system for external pipework, incorporating an external frost thermostat, should be considered. If such a system is used, the requirement to use 32mm pipe does not apply

• Internal pipe runs in unheated areas such as lofts, basements and garages should be treated as external runs

If you have identified a frozen condense pipe

1. Locate the frozen areas and thaw the pipe work. This can be achieved by using a warm pack often used for sore joints, a hot water bottle or consider if on ground level pouring warm water over the affected areas. Care should be taken to ensure any excess water on the ground will not create a slip hazard. Boiling water should not be used

2. When the condense pipe work has been fully thawed and drained the boiler can be re-started

3. Now that the heating and/or hot water has been restored, you need to identify what measures can be taken to prevent the pipe from freezing again. Certain considerations need to be made

Look for installation improvements

• Has the external pipe work been suitably lagged, and is the lagging approved for external use?

• Does the pipe work run externally 19mm or 21mm in diameter, consider increasing to 32mm

• Has the condense pipe got a long external run, can it be reduced?

• Could the fall of the pipe work be steeper?

• Is the termination point of the pipe exposed to wind chill?

• Consider trace heating, talk to your local merchants for advice

• Why was the condense pipe run externally, consider moving inside if at all possible?

Further information

Watch a demonstration video on how to unfreeze a condensate pipe

Date published: 29th November, 2010

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