Freeze Damage in Sprinkler Systems and How to Prevent It

Freeze damage happens on a winter night, not during a fire. And it has two outcomes: the pipe bursts (water damage) or an ice plug forms (the system is silently disabled). The second is more dangerous because it gives no sign at all.

Where it starts

Freezing starts at the coldest and most stagnant point in the system. The twelve highest-risk locations:

1. Lines at loading docks and just inside doors.
2. Branch lines close to external walls.
3. Unheated roof voids and service galleries.
4. Open-sided car parks.
5. Cold store entrances and lobbies.
6. Around control valves where the valve room is open to outside.
7. Low points in dry systems that do not drain fully (auxiliary drains).
8. Wet system risers running up an external wall.
9. Dead-end pipe runs where water never moves.
10. The external portion of a tank suction line.
11. Hose reel supply lines.
12. Shallow sections of external hydrant mains.

The options

Solution	Where it suits	Watch out for
Heating the space	Small, closable spaces	Heating continuity must be monitored, with a fault alarm
Dry system	Cold stores, open car parks, loading areas	Low point drainage and air quality are critical
Double interlock pre-action	Freezing plus accidental discharge risk together	Detection and pipe volume design become important
Antifreeze solution	Limited, small branches	Permitted solution types and ratios are restricted by the standard
Heat tracing	Local runs, around valves	With insulation; supply and fault monitoring required
Insulation	Not sufficient alone	Without a heat source it only delays freezing

A note on antifreeze: the permitted solution types and mixing ratios are restricted by the standards and have been narrowed over time. The solution type and concentration in an existing antifreeze branch must be verified against the current edition of the relevant standard.

The limit of insulation

Insulation does not generate heat; it only slows the loss. A pipe holding stagnant water freezes under insulation too, given a long enough cold night. Insulation is a solution only alongside a heat source — space heating, heat tracing or continuous flow.

Pre-winter checklist

1. Have all dry system low point drains been emptied?
2. Does the dry system air dryer work, and is the compressor cycling normally?
3. Is the heating running in heated spaces, and is its failure monitored?
4. Is heat tracing energised, with the fault signal reaching the panel?
5. Are valve rooms and the pump room above the minimum temperature?
6. Are runs along external walls insulated and undamaged?
7. Are loading doors kept closed, and do the air curtains work?
8. Do tank heating and level monitoring work?
9. Have dead-end pipe runs been identified and removed?
10. Are the points that froze last winter recorded, and has action been taken?

What to do if freezing is suspected

Where an ice plug is suspected, the pipe is never heated with an open flame. The correct approach is to isolate the line, heat it under control (warm air, electric heater) and check for leaks once it thaws. When a frozen line thaws, cracks formed during freezing appear, so a pressure test after thawing is required. Compensating measures must be in place for as long as the system is out of service.

Frequently Asked Questions

Can a dry system freeze?

Yes. The pipe is not empty; condensing moisture collects at low points. If those are not drained regularly an ice plug forms and the system is silently disabled.

Does insulation prevent freezing?

Not on its own. Insulation generates no heat and only slows the loss. It is a solution only alongside a heat source — space heating, heat tracing or continuous flow.

How is a frozen pipe thawed?

Never with an open flame. Isolate the line, apply controlled heat, and pressure test after thawing to check for cracks; keep compensating measures in place while the system is out of service.

Is antifreeze solution unrestricted?

No. Permitted solution types and mixing ratios are restricted by the standards and have been narrowed over time. Existing branches must be verified against the current edition.

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