Not strictly DIY but I know someone here may have an answer.
My parents are having quotes to replace their 26 year old boiler replaced. She's had two quotes, one using a Gloworm Flexicom 30SX and one with a Keston C40. The Gloworm quote is significantly cheaper and it's obvious when I look at the prices of the boilers on line. The Gloworms typically go for about £700 and the Kestons £1600.
Considering the fact that the house is a semi-detached period house (no double glazing etc.) that would happily house a family of five or even six are both of these boilers suitable and is the Keston going to be a lot better? Is its only advantage its increased power output or are Kestons generally better anyway?
Have a look at Viessmann too. I recently bought a system boiler from them for a four bed Victorian semi and it cost less than the 1600 quid you mention. It's beautifully made.
I've got a Keston C25 (no longer manufactured). I bought mine in 2002, probably about half way through the manufacturing life of that model. At that time, Keston manufactured only condensing boilers (even before they became almost mandatory), and hence their customers were primarily DIY people like me who were willing to spend money on technology, and local authorities who are spending someone else's money. (I believe they cam into this market from manufacturing large commercial condensing boilers.) They had a good reputation in the self-build groups for helping DIY installers, and offered a commissioning service. That all came to an end, parts became difficult to get, and it turned out there were parts in the boilers which weren't really up to the job (flue pipework and igniters being common failures). Keston seemed to have an improvement program (the flue pipe was changed at least a couple of times during the manufacturing life, and the ignitor at least once). I liked the technology, and it's a simple efficient unit. It's OK for me who can fiddle with it and replace bits that fail, but it's not a boiler I'd put in my parents' house, where it's just got to work.
Now I did see improvements throughout the manufacturing life, and if Keston have learned from the issues, it could be that their current boilers are wonderful now. I'd want to find some evidence of that before committing to another one.
I'd also check that there's a supply route for spare parts I can access (which rules out HRPC, and I think that was the only parts outlet Keston had). Condensing boilers are beyond most gas installers to diagnose and repair when they go wrong (excepting the ones here, but you're very lucky to find such a good one out in the wild). That means I have to do it myself.
Keston C40 sounds very large for a semi. If it's not doing instant water heating (as a combi does), I doubt you'd need any more than 20kW. A larger boiler won't modulate down as far (11kW is lowest for the C40, and about 7kW for my C25).
The Kestons are probably more sophisticated, but from what I hear on this group they aren't brilliantly reliable. And however smart they are I doubt they're worth double the price of a quite reasonable boiler. The others I'd consider (in the Glow-worm rather than Keston price range) are Worcester and Vaillant (who own Glow-worm).
Do you see much Keston kit come in, specifically the C25?
Of course, there's relatively little out there compared with the main stream makes. After they turned their back on the DIY/self-build market, and everyone else started making condensing boilers, they sort of vanished from the scene, which was a shame.
About the only advantage these days. Not sure about the Qudos reliability.
The Broag range are the best price/performance available in quality kit. Their control system is OpenTherm with weather compensation as standard, and beats all of those, although Viessmann and Keston do have OpenTherm. The Broag has a duel temperature boiler temperature system - calls for DHW and the boiler runs up to maximum temp, after it reverts to weather compensation. Broag are better than Vaillant...and much cheaper too.
Keston had a boiler that was super simple (forget the number) - discontinued around 2001. It never had a pcb. It was simple and never needed the heat exchanger cleaning either. A fit and forget model. When fitted to rads it cycled like hell, unless they were over large rads. Many selfbuilders fitted them to thermal stores doing UFH. Then they shined and never cycled at all. The perfect match for a store.
I put him onto it. It was always way ahead of all others on the control system, to the point it stood out - many are catching up, like Keston and Broag. It also modulates down to around 3kW. The lowest of any domestic boiler I know of, unless a few others have now reached this I don't know of.
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