Open-flue boiler replacement

[stewamax]

My existing old Thorn gas boiler still gives excellent service, but I need to plan for the day when it doesn’t.
Gas is fed from 22mm piping (with one gas fire tapped off it), so the gas supply should be adequate without re-piping, and the present boiler site even has a convenient indoor waste pipe to take the condensate without the risk of freezing.

But routing a new balanced flue from the existing boiler cupboard would be very difficult and it would have a long tortuous path with many joints (and hence many inspection hatches). Siting the boiler elsewhere would necessitate extensive re-piping for both gas and water.
The present open-flued boiler vents though a chimney with a seamless metal liner, and takes air from the room (which has approved air vents).

My house needs a substantial boiler (the Vaillant Ecotec 438 looks attractive), but such boilers all have a room-sealed (‘Cnn’) flue classification.

Is there any way to use the existing flue?

[Mike4]

Is there any way to use the existing flue?

Short answer: No.

Longer answer: It depend what you mean by 'flue'. If you mean your existing flue liner then definitely no. I'm a fault-tracer not an installer so not really fully informed about what's on the market, but I suspect it's still 'no' even if you mean just the brick chimney. There are one or two little boilers with a 'dual concentric' flexible flue (designed to replace back boilers in terraced houses) that replace the stainless steel flue liner you describe, but their output is feeble.

The Keston boilers that use UPVC waste pipe as flue tube can be installed with a vertical flue inside an existing chimney but current regs requiring access panels every 1.5m for visual inspection mean some pretty big and expensive holes will need making in the brickwork, all the way up to the top.