Keston Celsius 25 service modes

Hello folks, 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)?
Tim Mitchell
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     snipped-for-privacy@congoblue.co.uk writes:

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.
--
Andrew Gabriel
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Thanks Andrew,
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 difference.
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 play with.
How are you logging your boiler status at the moment - is that just by monitoring the front panel LEDs?
-- Tim Mitchell
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     snipped-for-privacy@congoblue.co.uk writes:

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 logged too.
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 [...snip...] 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.
--
Andrew Gabriel
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Thanks for the info Andrew. That's quite a sophisticated heating system you've got there!
-- Tim Mitchell
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