Regular or system to combi cost UK 2026
The going rate for regular or system to combi in 2026 is £3,000–£5,700 (total, ex VAT). Below: a calculator, what the job involves, materials at three price levels, and the prep that changes the price.
Regular or system to combi calculator
Market band source: Heatable.
What the job involves
| Stage | Task | Typical time |
|---|---|---|
| out | Drain down and remove old boiler | 2 h |
| out | Remove cylinder and loft tanks, cap off | 4 h |
| in | Re-route and cap pipework | 6 h |
| in | Fit boiler, flue and controls | 5 h |
| in | Power flush the system | 4 h |
Materials at three price levels
| Material | Budget | Trade choice | Premium |
|---|---|---|---|
| Combi boiler (A-rated, 25–30 kW) each | £750 Entry combi, 7-year warranty — Lowest cost compliant boiler | £1,000 Mid-range combi, 10-year warranty — Reliable, parts easy to get | £1,500 Premium combi, 12-year warranty — Quieter, better hot water |
| Magnetic filter and cleanser each | £90 Basic magnetic filter — Catches sludge | £130 Branded filter and cleanser — Protects the heat exchanger | £180 Dual-action filter — Best protection |
| Flue kit each | £60 Standard horizontal flue — Straight out the wall | £90 Telescopic flue — Fits the wall thickness | £120 Vertical or plume management kit — Awkward terminal positions |
| Heating controls each | £40 Wired programmable stat — Meets Part L controls | £80 Wireless programmable stat — Place it anywhere | £180 Smart thermostat — App control |
| Valves, pipe, fittings and condensate allowance | £50 Standard fittings — Connects up | £80 Fittings plus frost-protected condensate — No frozen condensate | £120 Full copper tails and lagging — Tidy, efficient |
| Conversion pipework and caps allowance | £180 Plastic pipe and caps — Re-route and cap off | £300 Copper re-route — Durable | £450 Copper plus new isolation valves — Tidy conversion |
| Power flush chemicals set | £40 Standard cleanser — Shifts sludge | £60 Branded cleanser and neutraliser — Faster clean | £90 Heavy-duty descaler set — Badly sludged systems |
Trade prices ex VAT, estimates checked 2026-09-25. Log your receipts in Grafto and your own prices replace these.
What changes the price
- Mains flow and pressure? good (tested) · poor · not tested big effect
- Bathrooms? 1 · 2 · 3+ big effect
- Controls? keep existing · new programmable stat · smart controls
- Gas pipe size OK? yes - 22 mm · no - needs upsizing · not checked big effect
Good practice
- Gas supply must be sized for the new boiler
Prep to look for
| Condition | Check | Effect |
|---|---|---|
| Sludge in the system | black water from a bleed valve, radiators cold at the bottom | Power flush the system |
| Microbore pipework | 8–10 mm pipes to radiators | Microbore: limits radiator upgrades and blocks easily — flush it |
| Possible asbestos lagging | old grey or white pipe lagging | Possible asbestos lagging: stop and test before disturbing |
| Lead pipe | dull grey soft pipe, wiped joints | Lead supply pipe: recommend replacement |
| Corroded fittings | green or white crust, rust on valves and pipes | Replace corroded valves |
Questions
How much does regular or system to combi cost in the UK in 2026?
The researched market band is £3,000–£5,700 (total, ex VAT), from Heatable. A worked example of 1 install comes to about £2,351–£4,245 across budget, trade and premium materials.
How long does regular or system to combi take?
The worked example of 1 install takes about 1.5 working days.
What changes the price of regular or system to combi?
Mainly mains flow and pressure, bathrooms, gas pipe size ok, plus any prep found on site: sludge in the system, microbore pipework, possible asbestos lagging, lead pipe.