Frozen Boiler Condensate Pipe — What to Do
9 out of 10 winter boiler lockouts on modern combis are a frozen condensate pipe — a narrow plastic pipe running to an outside drain that ices up first in any cold snap.
Make it safe — before anything else
Warm water only — never boiling
Boiling water cracks the plastic pipe. Kettle water left to stand for 2–3 minutes is perfect.
Boiler stays OFF during thaw
Turn the boiler off at the front panel while you thaw. Reset only when the pipe is clear.
One reset only
Repeated resets on a locked-out boiler can flood the combustion chamber. Once fired, one press, that's it.
Only Gas Safe registered engineers work on gas
Condensate is safe DIY. Any work on the boiler itself, the burner, or the gas supply is Gas Safe registered only.
What Kevin (our AI) will check first
Message Kevin and he'll ask exactly these questions before we send an engineer, so we bring the right parts on the first van.
- Boiler make, model and exact fault code showing.
- Where does the condensate pipe exit the property — kitchen wall to a gully, or up and over an eaves to a soil stack?
- Length and diameter of the external run — 22 mm skinny pipe is the worst offender.
- Any insulation / trace-heating fitted around the external pipe?
- Would you like us to re-route it internally so it never freezes again?
Common causes of a frozen boiler condensate pipe
Undersized external pipe
Old installs used 22 mm plastic outside. Current best practice is 32 mm+ or the pipe stays internal. First thing that freezes.
Long horizontal outside run
Every metre outside is another freeze risk. Long soffit runs to a shared soil stack ice up in mild frosts.
Bend or trap at the outside outlet
Water pools at any elbow or trap on the external run — freezes solid overnight.
Missing lagging
Foam pipe-lagging on the outside condensate is a 10-minute job — most installs skip it and pay for it every January.
Blocked outside drain / gully
The condensate discharges into an outside drain that's already blocked with leaves — water backs up into the pipe and freezes.
Honest cost band — why we won't quote blind
Typical
Free advice in chat — thaw is usually DIY with warm water and 10 minutes
Complex
On-site thaw and re-lag: £120 – £190. Re-route condensate internally: £220 – £420 depending on route.
We'd rather talk you through a free thaw than charge you for a 5-minute job. If it's re-freezing every week, book a re-route or trace-heating install — £50 diagnostic and refund-if-not-fixed apply.
Fixed £50 diagnostic
Flat fee. No hourly meter running.
Fair quote or refund
Transparent pricing — refunded if we don't fix it.
Vetted UK engineers
DBS-checked, insured, real reviews.
AI-triaged in seconds
KJ chats first so the right engineer arrives.
Related emergencies
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Heating lost overnight in a cold snap
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Boiler on but no heating
Emergency guide
See all in the emergency plumbing hub — or the leaks & water damage hub.
Areas we cover for frozen boiler condensate pipe
Same-day across Greater Manchester and Rochdale.
Frozen boiler condensate pipe — FAQs
Dealing with a frozen boiler condensate pipe? Chat with Kevin now
Real triage in seconds. £50 diagnostic visit — refunded if we don't fix it.
Related hubs: emergency plumbing, leaks & water damage, all services.
Chat with Kevin about Frozen boiler condensate pipe