More Keston Woes

[Richard]

My Keston boiler seems nothing but trouble. In the two years since I have had it installed, it has failed in the following ways

The main PCB failed (just stopped working)

The Keston system kit (expansion tank) failed- the membrane went

and now the cabinet overheats

Surprisingly the keston does not have a reset switch. Instead you have to replace the 'thermal fuse' which is set at £4.50

This is just to get the boiler to re-ignite. Then I surpose you have to test it and see why the boiler overheated. Proably blowing one or more of these thermal fuses. My local supplier tells me they do not stock these items. Keston naturally do not supply direct, and I am left with having to wait a week for this non stock item to appear (at a charge of £18.50! (£14 small order carrage!) )

Therefore I am forced to call on Keston themselves to fix the problem. It is going to be a very expensive repair (their MINIMUM is £150) as at least their engineer will have the parts to hand, and will not be on an endless cycle of get part, fit it , blow it discover real underlying fault, get part fit it etc etc. I cannot wait weeks in this weather.

So in conclusion. I cannot recomment kestion celcius 25s. Too flaky Richard

[Andrew Gabriel]

They're around 50p each from CPC if this is the one on the transformer connector block, but you'll have to know what the fusing temperature is, and I've never looked at it that closely. Manual mentions 82ºC, but the nearest standard values for thermal fuses seem to be 72ºC and 84ºC.

Well, the thermal fuse failure is just a symptom of something potentially more serious.

Let's try to guess what might cause the temperature in the cabinet to overheat. Perhaps blocked air intake or flue, burst/split/disconnected internal flue pipe, burst/split/disconnected internal condensate pipe before U-trap (would also show up as water leaking from casing), failed burner gasket, failed heat exchanger insulation (internal or external), excessive combustion rate.

Also, are there any external influences which might heat up the boiler casing, such as positioned over a radiator or some other heat source? This could have blown the thermal fuse by overheating the boiler when it's not running and there's no airflow through it.

[Andrew Gabriel]

I just checked the fault finding section, and it gives another possible cause as pump overrun not working although I'm not sure what you could do about that as it's controlled by the fan control board. You could perhaps have a system design which had no water path for overrun (e.g. no 3-way valve and no bypass) or the bypass loop is too short to absorb the required energy.

Another thought -- has the thermal fuse actually failed at all? Check it, and if not, look for a broken wire connecting it back to the fan control board. It could also be a fault on the board itself.

[Richard]

yep, whole host of possible causes. Hence:-

[Richard]

Thanks for your advice Man acme today, fitted new fuse and after 30 mins spooted micro leak in seal where flue attached to boiler. This is the black rubber gasket. It seems it is sealed by just silicon from a gun. If it lets water out, then it can cause a build up of steam in the cabinet thus causing thermal cut out.

So all working again. Must say next time its serviced I will get them to check the silicon seal.

Richard

[Ed Sirett]

Alas you seem to have got the lemon. I have now installed 3 C25s the oldest is nearly 3 years ago. None have had any trouble although the C40 had loads (But mostly suphide dust getting into the gas valve whcich was not Kestons's fault).

[Andrew Gabriel]

I can't picture a black gasket in the flue path. Was this the burner gasket -- the large rectangular gasket on top of the rectangular heat exchanger box? A leak at this point would be very hot, whereas a leak in the flue would be much less so.

I did replace the burner gasket on mine during servicing as a) it was impossible to get it off in less than about

10 pieces because it had been glued on, and b) it had hairline cracks through at several of the mounting holes (although I couldn't actually see any sign of leaking there). I didn't silicone in the replacement gasket as the instructions don't say this is necessary. I did check it again a week later to make sure it still looked OK with no sign of leaks/cracks. I bought a couple of them -- can't remember the price but it was under a tenner each.

Hum, did it look like it had corroded anything in the boiler (the steam is acidic)? The thermal trip probably caught it before it had a chance to do so.

If it is the burner gasket, this is supposed to be open at each service anyway, to clean the burner and surrounding area.

[Richard]

my teminology is not really accurate. it is a black ribbed tube going up to the flue outlet. The base of the tube should be sealed with silicone otherwise flue gasses/water can leak into the cabinet. The flue gasses are i guess not hot enuf to trip the overheat but the water can be turned to steam by the hot surfaces and im told fill the cabinet with steam and this would clearly trigger the overheat.

[worriedconsumer]

I bought a new Keston C25 boilers which was installed and commissione

in late December 05. The installation was inspected in January 2006 b a Keston engineer, and the boiler has been running well for the las four months, but more recently it appeared to be losing efficiency.

This evening I noticed a dark stain in the grouting in the tilewor fronting the room space space in which the boiler was installed. investigated and found that condensate had been dripping out of th boiler casing for what was clearly some time, judging by the highl evident level of corrosion to the flow control valves, pipe work boiler casing and damage to the room space area beneath the boiler.

I am an engineer by trade, so I felt confident in investigatin further. I removed the casing to find condensate dripping out of th fluted rubber vent tube to the right hand side of the combustio chamber. There was also a pool of rusty-coloured liquid in the botto of the boiler which spilled out when I pulled back the casing.

I investigated further and found the rubber flue tube to be completel corroded and brittle - the inner sides of the flutes have split so i is possible to stretch the pipe out like a slinky spring. I ran th boiler with the casing open and was shocked to see a huge amount o flue gas coming back into the boiler itself. The boiler casing i corroded in parts and very rusty looking, yet it is not even six month old. It - not surprisingly - runs very hot, too.

The boiler casing is not properly sealed, either. A quick check with smoke can showed that the positive pressure of the flue gas was pushin the flue gas out of the casing into the room cavity in which the boile is installed. This boiler room space is not vented to the outside - m installer informed me that the boiler is self-venting, allowing it t be installed in domestic spaces such as kitchen cupboards etc.

It is obviously a known design fault. I note - with a little bit o investigation on the internet, including posts in this threa describing a cracked 'gasket pipe' from January '05 - that the lates version of the C25 boilers no longer contains this rubber pipe and ha been redesigned with a solid one. This can only be because someon realised there was a serious problem.

My c> The Keston system kit (expansion tank) failed- the membrane went and no

-- worriedconsumer

[Andrew Gabriel]

Why did Keston inspect it only a month after installation?

There's a non-resettable case over temperature sensor which people have reported blows if the flue splits and discharges back into the case. It's mounted on the transformer.

My 2002 model has the black consertina pipe. I recall someone saying earlier ones had a blue flexible flue pipe which Keston swapped out. The black pipe in mine is still flexible (I had to disconnect it to clear a blockage in the condensation outlet). However, I have almost never run my boiler very hot; the temperature knob pretty much only went past pointing straight up (about 60C flow) during commissioning. In normal running, it is set pointing to the left (about 45C flow). I'm curious what position/temperature yours is normally set to -- maybe this has a significant effect on the flue pipe life?

[Ed Sirett]

My own is a 2003 model and has not had a problem in this area. I installed one the other week and this has a thicker solid un-reinforced one piece rubber hose from the bottom of the heat exchanger to the flue outlet spigot. It makes a slight deviation around the gas supply pipe.

When in operation with the cover on the internal air pressure is always less than ambient (although severe weather could alter this on a very temporary basis). This would be true even if the flue outlet hose splits within the boiler casing (a bad fault). As AG posted if it got so bad that there was a serious problem the boiler would shutdown.

The only condition which would make the outlet hose get subject to an over temperature would be running the boiler with no water in it (there is a low pressure cut out against this).

I agree that this is a real bummer but you should be able to get the replacement part fitted by Keston under warranty.