My Keston Celsius 25 makes a repeating banging noise in the pipework
from time to time. I've posted about it here before, but we never got
to the bottom of it - it sounds like some sort of pressure oscillation
in the pipes (possibly due to an undiscovered airlock somewhere).
Anyway I had a Keston service engineer come a couple of weeks ago,
using a jumper on the pcb he put the boiler into a service mode where
he could control the pump speed directly from the knob on the front
panel (but was sadly unable to identify the banging problem). He was
rather coy about telling me how to do this. I see there are some
Keston experts here - anyone know how to do it? It would be handy in
trying to sort out my problem.
Also I was interested in Andrew Gabriel's all-singing all-dancing
front panel replacement which he posted about in another Keston thread
in December, and status outputs available from the unit. Is there any
info about this anywhere (or any chance Andrew could email me it)?
Is this a sound like a large church organ pipe?
That happened with mine when mixture was way off (i.e. as delivered).
Otherwise if it's in the water pipework, sounds like kettling.
Either Ed or myself have posted the info before. It's got 3 test modes
and normal mode which you cycle round. To change mode, switch boiler
off at the knob, remove the jumper, and then momentarily switch boiler
on and off again. Each on-off transition moves it to the next mode.
Each test mode lights up a different LED. When you've set a mode, put
the jumper back on, and the boiler then operates in that mode. I can't
remember offhand the order you cycle through the modes, but the modes are
different modulation levels; variable according to the knob position,
fixed min, and fixed max. Some of the earlier boilers will have
difficulty igniting on the min setting (which they don't do when running
normally) and you may need to half block the air intake with your hand
until it ignites. Later boilers handle this by igniting on a higher
modulation level and then drop back to min once ignited.
You need to use the min and max modes to set the mixture with a flue
gas analyser. Unless you understand gas appliances, you shouldn't be
playing with the test modes though. I don't know what happens when the
boiler gets to max temperature in test mode -- I would hope it shuts
off, but it may be that part of the logic is disabled in test mode.
I haven't done anymore with it -- lack of time. Also, I was slightly
hesitant about playing with it during the guarantee period, although
that's run out now.
The status was simply the state of the 8 LEDs and the position of the
control knob, so these could be monitored by computer and reported
remotely. The inputs to the board were remote control of the knob by
using a motorised pot and and remote on/off switch (which had to be
separate, as I couldn't get a motorised pot with on/off switch).
All inputs and outputs were electrically isolated so nothing in my
computer control could send any damaging electrical signals into the
Keston. I tested it in the boiler and it worked, but I didn't leave
it in there.
Someone else (I forget who) also did a mod to the Keston front panel
circuit board to force it to full power (or more strictly, max temp)
when reheating the H/W cylinder, thereby having separate temperature
control for heating and hot water, something which the C25 lacks. In
my case, it only does the heating -- I have a separate multipoint
water heater for hot water.
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The noise is a bang-bang-bang noise about 4 times a second, it starts
when the boiler modulates down from full output to a low level
(usually 1 LED) and goes on for about 15-30 seconds, then it sort of
fades away. If you have the case off the boiler you can feel all the
pipework twitching. It only does it occasionally and I think it's only
when it's doing hot water only and the CH zone valve is closed. I
think the supposed air lock is in the return pipe from the hot water
coil, which does have a raised section in it where air could get
stuck. I have tried every setting of the bypass valve and the gate
valve on the CH coil but I can't find a setting which makes any
Thanks for the info about service modes. The keston engineer said that
it would cut out when the water reaches some maximum temp, though
you're cooking your radiators by then. As you say not something to
How are you logging your boiler status at the moment - is that just by
monitoring the front panel LEDs?
Sounds like it's on the water side, rather than the gas/air side.
At the moment (and since it was installed), I monitor and log the
two mains outputs from the connector block, which are burner on,
and lockout, and I generate the call for heat signal which is
I just searched back in the logs for a case where boiler lockout
had been triggered, which is November 2006, so I could show you an
interesting sample of the logfile. In this log, upstairs heating is
on, and someone has turned the thermostat up to 19.9C at 16:15:57.
It's not normally that high; I vaguely recall someone was staying
who didn't feel well, and it's obviously been left on overnight
which is also not normal as it automatically goes to setback when
everyone's gone to bed.
The computer control is aiming to keep the "Temperature - Upstairs"
to the "Thermostat - Upstairs" setting. Other temperatures are also
recorded in the log. Downstairs heating is off, which means it's
actually setback to 14C and so not triggered to come on in this log.
The person who wasn't feeling well was in bedroom 3 and had the window
open, which is why bedroom 3 is cooling off faster when the heating
cycles off. The bedroom 3 temperature is logged, but not used for
system control -- it's part of the upstairs heating zone.
Nov 12 16:15:57 Thermostat - Upstairs 19.9
Nov 12 22:47:14 Temperature - Bedroom 3 18.5
Nov 12 23:03:14 Temperature - Bedroom 3 18.0
Nov 12 23:21:31 Temperature - Downstairs 18.5
Nov 12 23:28:48 Temperature - Bedroom 3 17.5
Nov 12 23:32:26 Temperature - Upstairs 19.5
Nov 12 23:32:27 Output Upstairs Heating Demand ON
Nov 12 23:33:11 Input Boiler Burner ON
Nov 12 23:37:22 Temperature - Bedroom 3 18.0
Nov 12 23:42:09 Temperature - Bedroom 3 18.5
Nov 12 23:48:58 Temperature - Upstairs 20.0
Nov 12 23:48:59 Output Upstairs Heating Demand OFF
Nov 12 23:49:00 Input Boiler Burner OFF
Nov 12 23:49:35 Temperature - Bedroom 3 19.0
Nov 13 00:02:33 Temperature - Bedroom 3 18.5
Nov 13 00:15:58 Temperature - Bedroom 3 18.0
Nov 13 00:39:56 Temperature - Bedroom 3 17.5
Nov 13 00:42:28 Temperature - Upstairs 19.5
Nov 13 00:42:28 Output Upstairs Heating Demand ON
Nov 13 00:42:51 Input Boiler Burner ON
Nov 13 00:43:00 Temperature - Downstairs 18.0
Nov 13 00:47:19 Temperature - Bedroom 3 18.0
Nov 13 00:52:47 Temperature - Outside 10.5
Nov 13 00:53:00 Temperature - Bedroom 3 18.5
Nov 13 00:57:46 Temperature - Upstairs 20.0
Nov 13 00:57:46 Output Upstairs Heating Demand OFF
Nov 13 00:57:47 Input Boiler Burner OFF
Nov 13 00:58:19 Temperature - Bedroom 3 19.0
Nov 13 01:09:01 Temperature - Bedroom 3 18.5
Nov 13 01:23:39 Temperature - Bedroom 3 18.0
Nov 13 01:48:22 Temperature - Bedroom 3 17.5
Nov 13 01:56:47 Temperature - Upstairs 19.5
Nov 13 01:56:48 Output Upstairs Heating Demand ON
Nov 13 02:00:19 Input Boiler Burner ***OPEN-CIRCUIT***
Nov 13 02:00:19 Alarm Zone Trouble activated
The boiler lockout signal is used to generate an invalid state
on the Boiler Burner input, i.e. open circuit. (On an alarm sensor
circuit, that would be a tamper alarm, but this is just a monitoring
circuit.) It does however generate a silent low priority alarm,
which means it phoned me and told me "Boiler Trouble" at 02:00:19.
I can read more into the logs by experience too. I happen to know
that when the boiler is operating correctly and has cooled down,
the burner lights in 18 seconds of the demand signal being given.
If you look back in the log, at 23:32:27 it took 44 seconds to
light, and at 00:42:28 it took 23 seconds to light, both of which
means it didn't light first attempt. Looking back further, it was
taking longer to light for about a week before it failed. This
was caused by the ignition electrode having drooped away from the
burner (a common Keston fault, particularly on their larger boilers).
Some more detailed automatic analysis of the logs could have given
me several days advanced warning of boiler failure.
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