I'm looking to install a new boiler in a property which will have two bathrooms and am thinking that a combi won't be enough. The Keston Duet looks like a good solution but I've a couple of questions:-
Will I be allowed to install this myself if I get a corgi man to connect up the gas? (I'll be dealing with the building inspector anyway because I'll need to get him involved in installing the second bathroom)
Is there another boiler I should consider taking into account ease of installation, reliability and cost?
It has an unvented cylinder and a registered unvented ticket man has to fit the cylinder. They require annual service which costs.
This is what you need:
formatting link
a Glow Worm Hxi boiler (Vaillant inside)
Check out a Range or Gledhill heat banks/thermal stores and others too. They all make them.
DPS do the DHW only Pandora which is aimed at the unvented cylinder market with a directly heated CH system and heated cylinder. The Pandora is maintenance free and does not need an overflow pipe or mains connection - filled by hose and the screw tightened after.
Best get an integrated store (heat bank) and have the CH off it as well. Boiler and CH buffering. A Grundfos Alpha pump can be on the CH with TRVs all around and no wall stat. Fit a Magnaclean filter on the CH return to the cylinder. A store heats the house instantly as the stored hot water is pumped into the rads immediately, so an instant early morning heat up. The CH circuit may just need a small amount of heat, say 1kW or less. This is easy as the pump winds up and down to suit - no inefficient boiler cycling (wearing out boiler parts) as when on a direct rads system. A thermal store copes with part load brilliantly (the CH buffer). Decoupling the boiler (it only heats the cylinder in one long efficient burn) - again increases efficiency and longevity.
Both can be fitted by yourself as long as your are competent. You may want to get a Corgi Landlords certificate after to check out the gas aspect.
Except that heating a heat bank to high enough temperature for hot water may actually reduce the overall efficiency of the system since a modern condensing boiler runs more efficiently at lower temperatures. However there probably won't be any difference with cheaper boilers where their flow temperature is manually set: only the more sophisticated (and expensive) boilers which modulate temperature to suit load will take advantage of being able to run rads at lower temperatures.
Actually it just heats the _radiators_ (nearly) instantaneously: it'll still take the time it takes for convection to heat the rest of the rooms for the house itself to warm up. In most conventional systems the time taken to heat up the radiators themselves is far less than the time to heat the rooms after the rads have got hot.
An optimum-start programmable thermostat such as the new Honeywell CM907 (wired or wireless variant) is a better way to get the house comfortably warm by a given time. Actually any half-decent time and temperature control system, intelligently set, can give reasonable comfort and economy.
Boiler cycling is far less likely with today's modulating boilers, and starting up and shutting down don't usually "wear out boiler parts" - failure modes are many and various.
Boiler installation is notifiable: you must tell you Building Control Office and have the installation signed off by an inspector unless the installer is competent to self-certify it (as a CORGI registered installer would be).
That's a dodgy way of getting round having the installation done legitimately.
An old wives tale. The first thermal stores, with integral DHW coils, ran at 80C. non-condensing boilers are supposed to run at 80C too. So it all fitted in.
The plate heat X changed all that. They are so efficient they will be sending water back to the bottom of the cylinder below 20C. very nice for condensing. Modern stores run between 70 and 75C.
The less sophisticated the boiler the better. More reliable.
Those boilers are designed to run rads directly. Those that modulate to maintain a flow setpoint are fine. The Hxi has an element of load compensation however it will maintain a setpoint temperature. It appears to keep within its own Delta T, and dropping the flow to keep it within. As the temperature narrows and the flow is below setpoint it will gradually increase the flow temperature to max delta T. It attempts to keep the delta T as the flow temperature rises. That is what I have observed. The Glow Worm tech people don't quite know how it works, well those I have spoken to.
It still heats up much quicker because of this. Most houses in winter take
20 minutes, or more, to get all rads up to 80C. Having them fully hot within a few minutes is a great advantage; as people with combi boilers in 2 bedroom flats experience. The rads are warm in no time at all.
A CM67 can be put on the CH of a thermal store.
Most only go down to 5kW and most above that (the Viessmann goes down to
3kW). If the house is calling for les than the minimum the boiler will cycle.
Having the pump always on and a constant supply of hot water available gives finer control of each room by TRVs. If it only needs 0.05 kW that is all the room will take through the TRV. When a boiler is being cut out constantly this upsets the supply (flow) temperature and part load heat input to TRVed rooms.
Starting and stopping does. Constant energising of controls and starting of fans wears out parts quicker. I know of system with Minimisers in, some direct onto the rads, and others on stores. Those on stores sound like new after 6 or 7 years, the others rattle along and make kettling noises when the TRVs close off. Also on a heat bank or store the flow through the boiler is always full, and no short circuit through a by-pass valve, which are rarely set up properly, and reduces efficiency as hot water is passed back to the return reducing efficiency.
Part load inefficiency is a big thing as most systems for most of running time are on part load.
Most do not and just log it as they don't have the manpower.
Competent DIY is legitimate. You are implying it is not.
I have occasionally suggested Keston C25 here when people have been asking about condensing boilers. I fitted one in 2002, which I've been very pleased with. Keston had been very supportive of DIY installers, and had a service where they would come and commission their boilers, which made them popular with energy consious DIYers long before condensing boilers were compulsory. There is some significant collective expertise in them in this newsgroup. Keston stopped supporting DIYers this way sometime around 2003, which removes that particular attraction to the product.
However, I must now reconsider my previous support for Keston. I ordered a new ignition electrode back in November. I'm still waiting. According to HRPC, Keston don't have any and they are waiting for Keston to manufacture a new batch. To my mind, this makes Keston boilers completely unsuitable for domestic heating use, where all spare parts must be available in days at most. (Actually, I struggle to think of any situation where you could use a boiler which might be down for 2 months waiting for parts.) Fortunately, I was able to make the broken electrode work, or I would have had to chuck the boiler out and fit a new one.
This is rather a shame because I would like to fit another Keston in another house. I like the technology and I admire Keston's continuous improvement of it, but without a viable spares operation, the product isn't suitable for any use I can think of.
They were aiming for the selfbuild market which they were big in. If they neglect parts then they will fall under. It might be an updated part they are waiting on and when in stock will not be problem. Check it out. I like their designs though, and well made.
I wrote to their MD, Nick Stevenson, a year or so back after I'd had a condensate trap on order for a month from HRPC, pointing out that as lesser known player in the market it was even more important for them to get their act together wrt spares. I also mentioned that if he typed Keston Celsius into Google/Groups he could see what we were all saying about his company!
I got a reply saying that he didn't know why I had had problems with a complimentary trap. You are absolutely right: the key parts - gasket, igniter, flue hose and a few others should be on the shelf of every HRPC branch. Alternatively Keston should have told HRPC that if they couldn't provide a proper service, they, Keston, would supply direct and then instituted an order by 4 get next day service.
brand, Ford bought Jaguar. Keston were superb until the Celsius, then teething problems which appear to be solved now after many years. The parts situation should be better under a bigger company. Expect New Kestons to be sourced out of the Ideal parts bin. Whether they will remain a quality brand we will see.
Many of these questions are answered in the BoilerChoice FAQ. I presume the duet is a hook up between a Keston Boiler and their unvented cylinder (likely rebadged).
Out of curiosity, what sort of thing went wrong with it? Looks like it was a simple early condensing boiler, without any electronic controls, from Keston's website.
The early Kestons were super simple and reliable. A spiral tube heat exchanger with a downwards mounted burner. Many cycled like hell, but Keston said that was OK. Well they would. Mate them to a Thermal Store with anti-cycle control and they worked wonderfully. I really liked them.
They were not the quietest of boiler and were generally fitted in garages in larger houses.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.