Condensing boiler

[AlanSlough1970]

I need a new 38kW condensing boiler with weather compensation) and have singled out the Keston C40. (The Keston C25 is too small and doesn't have weather compensation.)

Does anyone have any comments, good or bad, on the Keston C40?

Keston recommend using this boiler with a Honeywell "Chronotherm" controller with Open Therm comms protocol. Again, i wondered if anyone had any experience to share regarding the Chronotherm.

Lastly, Keston distribute a 300L Spa cylinder to go with the boiler. Does anyone know who is the original manufacturer of the Spa?

Thanks, folks

[Martyn Pollard]

Other boilers with built-in weather compensation are; ATAG Blue Angel (shr-24), ATAG Premier and Viessmann Vitodens 100/200. Build quality from these two manufacturers is excellent and are well worth a look if you are still keeping your options open. Cost is going to be similar to C40.

The ATAG works slightly differently to most boilers(esp kestons) in that it 'modulates up' rather than power on at full whack then try to slam the brakes on to match the load. With the weather comp brain unit it will run most of the day at a low output (condensing) rather than a few hours at high rate. It also has a stainless heat exchanger which looks more like an engine block than the usual squashed circular design. I personally think this arrangement gives optimum operation when working at low outputs (3.9kw with the

24kw model). You get a 10 year warranty on the HE if its installed by approved engineer.

Viessmann use squashed circular design heat exchanger. If you go to their uk website you can request technical information and look up your local installer. You can buy viessmann through plumbcenter/PTS but I would suggest you find an installer who is familiar the boilers first.

[Doctor Evil]

There is also

who also do integrated compensators.

The Mikrofill Ethos 46 is in there too.

do modulate quite low which is a big advantage in some cases. They are new to the UK and service and parts may be a problem. Viessmann have been in the UK for a qhile now and only just got their act together.

If you want a solid simple high output condensing design then get an Archie Kidd boiler (the first in the UK in the early 1980s), and install an external weather compensator. One can be bought for £160. It will not modulate the burner as the integared boioer units do.

use a thermal store and have a weather compensator heat the store to what it dictates. Then a simpler, and cheaper, and potentially more reliable, boiler can be fitted that only heats the stored water mass. Then boiler cycling is eliminated. Also two cheaper, simpler boilers can be bought and coupled to the store which gives redundancy. I would tend to lean to this approach.

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[AlanSlough1970]

Thanks, Martin.

On this newsgroup, Keston seems to have a mixed reception. Atag hardly appears at all because it is so new to the UK

I've had a look at the Atag S-HR 35 which looks suitable. Do you have any personal experience with Atag? Would you say that it has better build quality than Keston?

[Martyn Pollard]

I have just concentrated on the S-HR 24 so far as I don't install too many high output units. The 35kw unit is exactly the same, but it has a slightly elongated heat exchanger.

I don't think I can say a bad thing about the ATAG boilers. The units are a slightly larger and they have a larger (80mm) twin flue system than keston, but I have come to appreciate that a long small flue often means noisier boiler. The ATAG units are very quiet especially as they are running at low modulation for a lot of the time. They sell a concentric flue, but having installed many keston c25's I now prefer the twin flue options anyway. The twin flue system is plastic and plumbs in easy.

You can tell a lot by looking inside a boiler and the blue angel is so well constructed it is a shame to put the case on it. The control pcb hinges out for easy access and layout of the boiler makes servicing extremely easy. They have just started supplying an upgraded roomstat (they call it a Brain!) which also provides a programming interface to the boiler. I think they also have a solution for controlling the boiler over the internet although I've not seen one of those units.

The blue angel boilers have a built-in 3 port valve which means external control gear is reduced for most common installations. They have an add-on package solution for controlling S and S+ systems. They have a combi version in both blue angel and premier units, although if you're in the combi market its unlikely you'd be budgeting for this class of boiler.

ATAG boilers have been in the market for many years, although the distribution has been limited. They are now playing catch up and building up their customer base. I installed a Blue Angel boiler 1997 and the design has not changed since then.

I'd suggest you get some more information on the boilers and get some references from people who have them installed.

(seems under construction). Their number is 01243 673888 and if you mention I gave you their name they might not be too surprised why they suddenly get a rush of enquiries from uk.diyers ;-)

Martyn

[Ed Sirett]

This is not my understanding of how the Keston (C40) works. It ignites at about at a gas rate in excess of the minimum (say about 25% up the modulation range). It then operates at this moderate rate for about 30s or so 'testing the water' then ramps up to the required setting. It does not IME just go to 'full whack'.

My other comments are:

High powered boilers are unduly expensive presumably due to lower production volumes.

The C40 is setup out of the box to work with 70C max flow temp for sub zero outside temperatures. The consequence is that on milder days the boiler will reduce the flow temp to the point where it has almost no effect. This is adjustable but you need to be aware of it.