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How to fit a condensate pump

Updated: 22 October 2026

You have a condensate route that must climb before it can fall to a drain, and the pump on the doormat has a plastic tank, barbed outlets and flex with no moulded plug. This how to fit a condensate pump guide sets the physical sequence a householder can follow, then stops where UK wiring colours, boiler safety circuits and Gas Safe law take over. Acid, freeze risk and Approved Document H sit on the [boiler condensate pump](/hub/heating/condensate-pump/sub/condensate-pump-boiler) page. This text assumes the pump already matches lift and duty on the [condensate pump comparison](/hub/heating/condensate-pump). The instruction book in the box still governs. A qualifying purchase can earn a commission at no extra cost to you.

You have a condensate route that must climb before it can fall to a drain, and the pump on the doormat has a plastic tank, barbed outlets and flex with no moulded plug.

Our top picks

Grundfos Grundfos Conlift1-LS

Best overall

Grundfos Grundfos Conlift1-LS
8.8/10about £71.28
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Aspen Pumps Aspen FP3349 Max Hi-Flow

Rank 2

Aspen Pumps Aspen FP3349 Max Hi-Flow
8.8/10about £85.00
View offer
BAOSHISHAN BAOSHISHAN QS-360L

Best value

BAOSHISHAN BAOSHISHAN QS-360L
6.0/10about £59.99
View offer
On this page
  1. 1.Check the route before you buy a fitting
  2. 2.Set the tank
  3. 3.Power and the safety wires
  4. 4.Test with water, then stop

Check the route before you buy a fitting

Measure vertical lift from the appliance drain to the highest point of the discharge tube, then plan the fall into an internal waste your guidance allows. Head on the listing is that rise, not the metres of pipe on the floor. If the pump inlet sits above the appliance outlet, condensate may never enter the tank. Boiler condensate is warm and acidic. Tipping it into a rain butt or garden soakaway is not an Approved Document H route in England. A long external pipe still needs insulation and bore, because a pump indoors does not fix an iced outdoor leg. Match the listing’s orientation. BAOSHISHAN’s QS-24B split unit must stay horizontal and must not be inverted. Mini pumps with 70 ml or 0.07 L tanks tolerate little tilt before floats misread the level.

Set the tank

Mount the reservoir so vibration does not walk it off a shelf. Use the fixings supplied where reviews mention wall brackets and hose clips. Grundfos texts in the file mention hose and wall hardware. Keep access to the float chamber and inlet screen. Connect the appliance drain with the tube size the listing names, often 6 mm, 8 mm, or 21–27 mm on tank pumps. Support long horizontal runs so sags do not trap pockets. Fit the non-return if the listing includes one. AirTech prints a check valve on the barbed outlet. Reverse it and water runs back while the motor never rests. Leave room to clear debris. Stuck floats dominate the fault notes in this set when the float cannot travel.
Grundfos Grundfos Conlift1-LS

Testsieger

Grundfos Grundfos Conlift1-LS
8.8/10about £71.28
View offer

Power and the safety wires

Several pumps in this UK batch arrive with bare flex. UK reviews of the Aspen FP3349 report bare wires and no 1 A fuse in the box. An Ejoyous buyer fitted a BS 1363 plug and joined control wires so the switch stayed on for a dehumidifier trial. That is one owner’s report, not a wiring diagram. UK fixed wiring colours are brown live, blue neutral and green-yellow earth, not red and green as on a QS-24B diagram that put a UK reviewer off fitting the unit. Adding a fused spur or altering a kitchen ring is Part P work. Use a registered electrician if you are unsure. A normally closed safety contact is meant to open the boiler live when the high-level float trips. Do not bypass it, and do not connect it by guesswork. If the pump serves a gas appliance, book a Gas Safe registered engineer whose card covers boilers and matches the job. Aspen prints a 3.0 A normally closed switch, and the manual still has to show which terminal pair is which. A listing that only says safety switch, with no amps, gives you nothing to compare with the boiler instructions.

Test with water, then stop

Bench-test with clean water if the manual allows. Pour slowly until the float starts the pump, and watch the outlet into a bucket until the float stops the motor. QS-24L’s UK review describes continuous running when the float failed to cut out. Check barbs and clips, then run one heating or cooling cycle under observation. If the pump short-cycles, hums without moving water, or runs hot like a QS-24B report, isolate at the mains. Do not run the pump dry, and do not leave bare terminals exposed after a temporary test. Water on the floor after a successful jug test points at the route or the non-return, which condensate pump not working walks in order. If a gas boiler will not reset after the work, call Gas Safe. Spec checks before you buy sit in the condensate pump buying guide.

Common questions

Can I fit this on my combi myself?
Physical mounting and tubing on a dehumidifier or split unit may be within a competent DIY scope. Altering boiler condensate routes and safety wiring is Gas Safe work.
What does a normally closed safety switch do?
It keeps a circuit closed while the pump is healthy and opens when a high-level fault demands the boiler or appliance to stop. Exact terminals vary by model.
The flex has no plug. What now?
Terminate into a suitable plug with the correct fuse if the manual allows portable use, or into a fused spur installed by an electrician. Do not use travel adapters.
Red for live and green for neutral: is that UK practice?
No. UK live is brown, neutral is blue, and earth is green-yellow. If the diagram conflicts, do not energise the pump.
Where should the tube end?
At an approved internal drain or other termination your building guidance and appliance manual allow, not an outdoor hose into a butt for boiler condensate.
How do I test it without running the boiler dry?
Use a controlled water pour into the tank per the manual, or a short heating cycle once the plumbing is tight.
Does the pump have to be level?
Yes for many floats and split layouts. QS-24B explicitly requires horizontal placement.
When do I stop and call someone?
At bare boiler terminals, at a tripping safety switch, when the boiler locks out, or when wiring colours and manuals disagree.

Related pages

Best condensate pump

Condensate pump

Boiler condensate pump: gravity, acid and Gas Safe

Condensate pump buying guide: check duty, lift, tank

Condensate pump not working: float, tube and freeze

Sources

Public UK and manufacturer sources named below. amazon.co.uk prices, stars and review counts on these twelve listings were taken from the listing files. Page updated October 2026.

  1. Approved Document H, drainage and waste disposal (retrieved 21 October 2026)
  2. HHIC condensate discharge installer guide (retrieved 21 October 2026)
  3. HHIC condensate pipe guidance news (retrieved 21 October 2026)
  4. Gas Safe Register FAQ (retrieved 21 October 2026)
  5. Aspen FP3349 tech sheet (retrieved 21 October 2026)
  6. Grundfos Conlift1 LS data (retrieved 21 October 2026)
  7. CoolEasy condensate pump buyer's guide (retrieved 21 October 2026)
  8. condensatepump.co.uk boiler note (retrieved 21 October 2026)