In considering which boiler to install in the spring/summer 2008, I was impressed by the comments made on the above boiler and subsequently downloaded info for installation and service from the Keston site, however, I have a number of observations/ questions which I would be grateful to receive comments/enlightenment upon.
Flue arrangement. In my situation I would like to install a balanced flue which would rise vertically above boiler and terminate above a sloping tiled roof, I note that the Qudos has two separate pipes, one inlet, and one exhaust, which are physically separated by about 9 inches or so. One of their diagrams shows the two pipes to be terminating separately above the roof. My limited experience had led me to believe that balanced flues were arranged concentrically so that both pipes terminated in an area of equal pressure and I thought that was important to achieve.
Boiler location. Again in my situation, I would like to locate the boiler within a (not yet built) larder size cupboard with a full size door opening internally onto a central corridor in my bungalow. I note from the Keston literature that:
A) The compartment must be constructed in accordance with BS6798 (have not yet consulted this document at my local Library)
B) The wall on which the boiler is mounted must be of a suitable load bearing capacity and must be non-combustible. Question, would a standard
4insX 2ins timber stud wall having (internally)two layers of 12mm plaster board meet this requirement?
They were concentric to have all inside one pipe. A fan eliminates the need to have the two pipes the same length. The air intake can be taken say from below a suspended wooden floor and out to atmosphere on the outer wall at low level, while the products of combustion can terminate over the roof tiles. All using plastic drain pipe, the higher temperature grade.
Do you have a suspended wooden floor on the ground floor?
This model may not be the best for you. What are DHW requirements? Shower(s), bath(s), do you have a good mains pressure? How many people? CH requirements? Etc?
I'm after a system boiler not a combi version, I have an existing system boiler ( on it's last legs)which was installed in the garage ( :-( long pipes to the house). Installed an oil boiler in previous house with AQ6000 controller which I liked very much, hence the interest in the Qudos with the open therm link to a compatible controller which will give me what the AQ6000 gave me i.e
2Stage frost prot, Pump & valve exercise, optimisation, DHW control, Pump overrun,Outside temperature compensation, display of external temp, internal temp, flow and return temp. I think that's all I need (No perhaps desire would be a better word) unless I've forgotten something. Regards Don
Wrong answer :-) What you need and what you want maybe very different. Trying to help here. Do have a cylinder, power shower pump, etc? How old are these? There are stored water thermal store/boilers around giving mains pressure DHW and others doing similar. And many can hitch up a Chronotherm OpenTherm compatible controller. You could still have unitised thermal store/boiler in the garage and a secondary circulation DHW loop from garage to house, totally eliminating DHW time lags, and fill up kettles with instant DHW to reduce electric bills. And removing tanks and cylinders inside the house.
Look at the Atmos range of boilers. Excellent and super reliable. And they can hitch up a Chrontherm Opentherm compatible controller too.
No I am inclined to think that you are providing the wrong answers after all I was asking the questions :-))
No sorry, aluminium heat exchanger? Do you have a connection with Atmos? However, thanks for the info you added a third boiler to my list, Viessman are still tops. I read somewhere in the dim and distant past that the cost of a new boiler a very small fraction of the cost of the fuel it will consume during it's lifetime even more apt these days.
Not in this case. The combustion van is much more powerful than in most. conventional fan assisted boilers. The only no-no is putting the terminals on opposite sides of the house. (It would probably work fine in any weather except a hurricane) but the law (GSIUR 1998) explicitly forbids this practice.
I believe that a copy of this can be found on the interweb, if you search around. I used to hose copies on my web site until the BSI felt my collar. Essentially this means providing adequate ventilation for the cupboard. I'd guess 9^28 about 250cm^2 at high and low level to the room. Or half that to outside. This is not good it make this model cupboard unfriendly relative to it's competitors.
Keston will say yes or no. I'd be happy to install one like that provided at least one of the fixings found the wood.
Point taken, but the fan will use more energy presumably?
The only no-no is putting the
Yes, I thought that a room / cupboard containing a "proper" balanced flue boiler did not need external ventilation provided it is of a certain minimum size/volume, is this correct?
I would make sure that all the fixings would find the wood, I was more concerned about the combustion aspect, I believe that there is a British Gas document DM2 which may be applicable, but unfortunately I have not been able to have a sight of one. Many thanks Don
LOL, you haven't taken long to find the lie of the land here ;-)
Beware also of suggestions to draw combustion air from underfloor spaces, on other Keston products this use is specifically excluded on pain of voiding the heat exchanger warranty and whilst this is not specifically stated on the Qudos it does prohibit use of air from the inside a ventilated boiler-room so I'd say the same intent is there; to discourage potentially dirty air sources. I'd chose outside air if at all possible.
Drawing air in from underfloor spaces is excluded anyway. Running an air intake pipe through the space is and the space is a very useful mean of hiding then pipe. See makers.
If it's any help I fitted a Vitodens 300 earlier this year and am very pleased with it. Too early to tell the fuel savings over my old RS cast iron unit but looking good so far.
I doubt it will last as well as the previous boiler which did near 30 years with only a couple of thermocouples replaced - but I'm keeping my fingers crossed. ;-)
I don't know if the parts and general reliability has been improved with this new boiler. The C25 after a few years is turning out to be shockingly bad in this respect. I installed a maybe 20 of them in 2004/05 and many have had problems. One customer told me he had spent up to £800 repairs through keston. Another installer was recently asking me if I had secondhand c25 as he had a tandemn install only 2 years old, with numerous problems and repairs - I recall him saying the condensate traps were disintegrating. He felt too embarrased to tell the customer they really needed to replace them so was funding this himself as a stop gap to keep them going a few extra years before taking the replacement line.
I have only been maintaining one C25, for a friend, and had the case off it last week. It is looking in a very sorry state. Air vent leaking, internal flue pipe looks like its ready to disintegrate, case rusting inside. Also very handily the burner gasket has to replaced every time you remove it for cleaning - thats if you can remove the two nuts off which are obscured by the fan. I'm going to replace it for them in the summer in anticipation of future problems. I now only recommend Viessmann or Atag boilers and touch wood haven't had any problems with those makes.
The boiler does not need any air supply for combustion, but if it's installed in a cupboard then ventilation (quite a lot) is needed for appliance cooling.
Most makes seem to specify no additional ventilation, the fact that the Qudos 28 does needs it seems to be a big minus.
My experience having installed 5 units has not been a bad as yours. One unit had the gas valve go seriously wrong. The gas valve seems to drift of the ideal setting quite easily.
On my own unit nothing has gone wrong much. The gas valve seems to need tweaking from time to time to get the boiler on the right mix. The igniter seems to slowly droop down in the flames so that after a while (4 years for me) it stops working reliably.
The trap seems to collect gritty gunge which needs to be cleaned out from time to time. It's really hard to beleive that this gritty gunge must come /through/ the burner.
They are difficult to service (the fan has to be removed from the burner to let the burner be unbolted). The gasket is hard but has not cracked on my unit.
I installed mine 5 years ago. It's had a few issues, but nothing major.
First few things were manufacturing faults I picked up during and shortly after installation.
1) The internal drain c*ck leaked where it was screwed into the brass fitting. Fortunately I detected this during an air pressure test of the system, so no water leaked out and it was easy to remake the seal.
2) The supposedly factory-adjusted gas mixture was miles off. On comparing notes with others here, this seemed to be the case with all the C25's fitted. I invested in a flue gas analyser and set it correctly. (The installation manual does not contain sufficient instructions for doing this -- I had to get the proper instructions from Keston.)
3) The flue spigot gasket didn't allow for the bumps from the captive nuts, which meant it couldn't seal. I had to carve some extra bits out of it. I mentioned this to Keston afterwards and they said they've fixed that. I noticed on a newer C25 the spigot now extends into the boiler, whereas on mine it was flush with the top. This would also help here.
4) The flue spigot leaked condensate where they had glued the stainless steel to the muPVC collar. This left a small amount of condensate trickling through the casing for a few days before I noticed. I broke apart the supplied flue spigot and made my own using the original stainless steel part and made up my own muPVC collar with an internal recess for bead of high temperature acid resisting silicone sealant. This has worked fine. The leaking condensate was spotted before it did any damage to the casing. (After this, I advised here of an additional commisioning step of leaving a hose pipe trickling into the flue terminal for half an hour and ensuring no leaks from anywhere.)
During running, it's had 3 breakdowns. Two have been caused by the condensate exit from the heat exchanger becoming blocked, causing the heat exchanger to start filling with condensate and making a girgling noise until it blocks the flue outlet and then the boiler goes into lockout. The blockage may be caused by small pieces of the thermal insulation at the top of the combustion chamber breaking away. After the second time, I instigated a program of pouring a couple of pints of water into the flue terminal twice a year to flush out any debris in the bottom of the heat exchanger, and it hasn't happened again since. (It also flushes out debris in the condensate U- trap, but I've never seen that build up to anything like the amount required to block it.)
The third was caused by the ignition electrode drooping. It would light the gas but was taking more and more attempts to do so. Eventually it was too far from the guaze to detect the flame and although it lit, the controller shut it down thinking the flame had gone out. This is apparently a common fault with the larger Kestons, but less common with the C25. I managed to repair the ignition electrode for the 3 months it took Keston to make some new ones, but if it hadn't been repairable, 3 months to get spare parts would have written off the boiler.
I would find evidence of water staining in the bottom of the case when I opened it, but no sign of any leaks. Eventually I tracked it down when I was operating the unit with the cover off. It's hard up against a wall on the right, which was plastered but not painted. After the unit has shut off and finished it's purge/cooling cycle, a large wet patch starts appearing on the plaster right opposite the air intake tube. This was caused by moist air from the damp heat exchanger convecting backwards through the combustion chamber when the fan has switched off. With the casing on, this would condense inside the casing and cause the slight staining in the bottom. Having discovered what it was and that is was benign (not flue gas condensate or primary circuit water leaking), I ran a bead of silicone around the inside corners of the casing bottom to protect the edges from this moisture (some rust staining was just starting to show on the inside at the edges of the folded enamelled steel).
We had one or two cases of the flexible flue pipe failing in this newsgroup. Keston have changed the design 3 times. The first was a blue concertina tube. This was superceded by a black concertina tube (which is what mine came with). This has been superceded by a molded rubber hose. I ordered one of these and replaced the black concertina tube at the last service, although mine wasn't showing any signs of failure.
The ignition electrode design changed -- the replacement had a longer ceramic support but was shorter overall IIRC. I've just got another spare one, which looks to be different again and comes with the EHT lead, and replacement fixing screws and gasket (which I ordered separately last time).
I concur with your experience with the burner gasket -- it cracks into about 20 pieces when the boiler is used, so there's no way it can be reused after taking the burner out. I keep some spares.
I may have been luckier than some as my Keston is set to heat the water to only 45C most of the time, which probably stresses the system much less than if it was running at 80C all the time.
My Keston is controlled by a computer which also reads back the burner and lockout outputs, and keeps a log. When the system is operating correctly, the burner lights in 18-19 seconds of the call for heat signal if the circulating water is cooled down. If this time increases, it's a good indication the system is heading for trouble, and not lighting first time. I can also see some bugs in the Keston firmware. If the call for heat signal is active only for a short time (e.g. half a minute), at the end of the 2 minute purge/cooling cycle, the boiler will sometimes fire up again for a few seconds when there is no call for heat. It can repeat this up to 3 times over the following 6-7 minutes. On one occasion, it failed to switch off when the set water temperature was reached, but just got hotter and hotter until my computer dropped the call for heat signal (which happened before the water got to max temperature, fortunately).
As a boiler for me, I like the Keston (particularly the extra montoring outputs) and I can live with its breakdowns. I also designed and tested a replacement front panel PCB which allowed full remote control (including water temperature adjustment) and remote monitoring/logging of the front panel indicators, although I never put it into real service. I can see that Keston have been continuously improving it over its manufacturing life. Keston were well known for their support of DIY installers in the early days (their customers for domestic condensing boilers before they were mandatory were in a significant part DIY), although this DIY support no longer exists today. The bad parts supply situation I and others experienced up to a year ago was not the case with my last parts order a few weeks back, so I hope that problem is sorted out.
I also look after other boilers around my family, and it wouldn't be suitable for any of them. The reliability of the boilers they have is much higher, and needs to be so.
I doubt it would get through the burner. I suspect it's formed from the combustion products. Not seen it in mine though.
I don't remove the fan from the burner. I bought a set of short ring spanners from Halfords which fit quite nicely (although a couple of the nuts are a bit fiddly).
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