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Condensate pipe

Checked against its sources: Updated

A condensate pipe is the plastic waste pipe that carries water from a condensing boiler's flue gases to a drain.1 Makers say it must stay clear and must not be altered by anyone unqualified.23

Covers
Condensing gas and oil boilers, UK. Wording varies by maker.
You
Look at the visible pipe for blockages or faults, where the manual asks for that. Thaw only as a maker's guide allows.
A professional
Any change of route, length or fixing, a pump, trace heating, or a blockage that cannot be reached from the ground.

1 What the pipe does

Ideal's Logic and Logic+ guides say the boiler's high efficiency produces condensate from the flue gases, drained through a plastic waste pipe at its base1. Every condensing boiler needs a route like this. Worcester adds that the condensate is discharged regularly by a syphon inside the appliance2.

Pipe sizes, falls and routes are not given in the user documents read, so none are given here. They belong in the installation instructions and with the installer.

2 What makers tell users

Condensate pipe wording in user documents
Maker and documentWording
Worcester Greenstar i ErPPipe "must not be blocked or altered in any way"2
Main Eco CompactOnly a qualified professional may alter or re-route it3
Vaillant ecoTEC plus, 2023Regularly check the pipe and tundish for faults and blockages; have any fault eliminated by a competent person5
Baxi PlatinumKeep the drain unblocked and unmodified; E28 groups a blocked flue and blocked condensate with other faults6

A blockage can show up as a fault rather than a visible problem. Worcester's Greenstar i ErP table lists a blocked condensate outlet as one possible cause of the EA code, alongside a gas supply problem and a blocked flue, and says to check the outlet only if it is safe to do so7. Ideal's Logic+ gurgles and then displays "Ignition Lockout" when the pipe is blocked8. See reading a fault code.

3 Freezing

Worcester warns that pipe run externally or in an unheated area such as a garage can freeze even if well insulated, and that a frozen pipe shuts the boiler down4. Thawing is covered under frozen condensate pipe, which keeps to ground-level pipework and warm water.

Longer-term fixes are for the installer. An October 2018 leaflet endorsed by the industry's trade council prefers routing to an internal drain, or a freeze protection product9. The Main Eco Compact guide lists accessory trace heating elements for the drain pipe, and a combined pump for condensate and relief valve water, as parts rather than user tasks10.

Sources

  1. Logic Combi Users Guide, Ideal, 2013 file, introduction, third-party copy read 3 November 2026; the Logic+ guide of May 2014, UIN 204979 A07, p4 has the same passage.
  2. Pluming and condensate drain, p29, Worcester's i ErP guide, March 2015 read 3 November 2026.
  3. Operating principle, p12, Main Eco Compact, 7716571-04 read 3 November 2026.
  4. Extreme cold weather, p16, Greenstar 4000, September 2020 read 3 November 2026.
  5. Vaillant ecoTEC plus VU, VUW and VUI ..CS/1-5, document 0020308119_03, p16 read 3 November 2026.
  6. Baxi Platinum Combi 24, 28, 33, 40 guide, January 2018, pp7-8 read 3 November 2026.
  7. Fault table, p24, Worcester's i ErP guide, March 2015 read 3 November 2026.
  8. Logic+ blocked pipe passage, p12, Ideal, UIN 204979 A07, May 2014, third-party host, read 3 November 2026.
  9. HHIC-endorsed customer leaflet on frozen condensate discharge, October 2018 read 3 November 2026.
  10. Accessories list, p13, Main Eco Compact, 7716571-04 read 3 November 2026.