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Author Topic: Boiler Short Cycling  (Read 409 times)

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Sir Tigger QC

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Boiler Short Cycling
« on: 11 November 2019, 21:07:57 »

My 25 year old Potterton Profile keeps cutting out.  :'(

It starts up OK and runs for a while, but then shuts down for a while before starting up again.  Sort cycling I believe is the technical term.  :)

All the radiators get hot when it's running, it kettles slightly but just a mild hiss, and the thermostat appears to work.  :-\

It was running fine until Friday night when I got home after a few days away and the house was a chilly 12 degrees, so I whacked the power up to max from 3 and  all seemed well.  Ever since though...  :(  If I have it on 3 it doesn't warm the house very well at all, on Max it's OKish, but it's not right!  ::)

It's chewed a few PCB's over the years, so maybe it's time for it's next one?  ???  ::)
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redelitev6

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Re: Boiler Short Cycling
« Reply #1 on: 11 November 2019, 21:27:51 »

My 25 year old Potterton Profile keeps cutting out.  :'(

It starts up OK and runs for a while, but then shuts down for a while before starting up again.  Sort cycling I believe is the technical term.  :)

All the radiators get hot when it's running, it kettles slightly but just a mild hiss, and the thermostat appears to work.  :-\

It was running fine until Friday night when I got home after a few days away and the house was a chilly 12 degrees, so I whacked the power up to max from 3 and  all seemed well.  Ever since though...  :(  If I have it on 3 it doesn't warm the house very well at all, on Max it's OKish, but it's not right!  ::)

It's chewed a few PCB's over the years, so maybe it's time for it's next one?  ???  ::)
You've had your monies worth out of it ! just might be time for a new one ? 
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Sir Tigger QC

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Re: Boiler Short Cycling
« Reply #2 on: 11 November 2019, 21:48:21 »

You've had your monies worth out of it ! just might be time for a new one ?

 :o  ::)  ;D
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Fuse 19

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Re: Boiler Short Cycling
« Reply #3 on: 12 November 2019, 07:41:41 »

Never seen a Profile actually take out the PCB, its usually the 3 electrolytic capacitors dry up which cost sub a quid to replace (with higher temperature ones).

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Shackeng

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Re: Boiler Short Cycling
« Reply #4 on: 12 November 2019, 08:10:28 »

How long since system flushed and inhibitor added? Is there gas in the system?
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YZ250

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Re: Boiler Short Cycling
« Reply #5 on: 12 November 2019, 10:15:32 »

Kettle'ing is normally pump related. Prior to fitting a new pump on my system a few months back I flushed the system. Three months later the kettle'ing/short cycling/struggling to heat rads started again so I dismissed the pump as it was brand new. I eventually took the pump apart (very easy on Grundfos, just 4 bolts when you've isolated the water) and found rusty particles from the flush out clogging the pump impeller. Cleaned the impeller out, reassembled the pump and it's back to super hot again now.  :y  Far short of replacing every radiator on the same day I'm stuck with rusty particles floating around my system so, as the pump is so easy to clean out once isolated, I'm going to clean mine out once or twice a year from now on (famous last words, I bet I don't).  ::)

Worth a shot anyway.  :-\
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Sir Tigger QC

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Re: Boiler Short Cycling
« Reply #6 on: 12 November 2019, 11:27:46 »

I flushed it, ran a cleaner through the system (Sentinel X800) for a couple of days, flushed it a again twice and then refilled it with Sentinel X100 last January as it was kettling quite badly and it settled down after this.  :y

When I say it's kettling it's very mild compared to how it was and the boiler was working fine until I fiddled with the power knob.  :-\

The system does need bleeding from time to time though, and I can generally hear some air going through the pump which I've tried to bleed from the pump itself, but with little success.  :-\  I guess even the mild hiss though is the sound of gasses being produced.  :-\


Never seen a Profile actually take out the PCB, its usually the 3 electrolytic capacitors dry up which cost sub a quid to replace (with higher temperature ones).


I think Kevin mentioned this to me last time it played up and I still have the last PCB that was changed somewhere, so I'll dig it out and have a go, as I've found a guide as well.  :y

https://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler





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dave the builder

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Re: Boiler Short Cycling
« Reply #7 on: 12 November 2019, 11:34:06 »

not familiar with the antique you mention but YZ250 is on the right track by the sounds of it  :y
poor circulation is overheating the boiler either switching the overheat stat or over run stat
could be the pump,or blocked heat exchanger or pipework
is it closed loop or header tank fill ?
sounds like a good flush through and check the pump would not go amiss
obviously , care should be taken not to dump water all over the electricary gubbins (so isolate)
and don't dick with gas settings or connections
IF it is a gas related problem,like modulating gas valve bummed ,you should pay and have a "gas safe " engineer to rape you  ;D

even though you flushed it in january, you can't rule out sediment of a 25 year old system being flushed from a rad and blocking the boiler ,say when some inpatient **** whacks the boiler up on a Friday after being away  ;D :D
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Raeturbo

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Re: Boiler Short Cycling
« Reply #8 on: 12 November 2019, 12:18:06 »

Ha ha, it was cold mind ::)
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Sir Tigger QC

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Re: Boiler Short Cycling
« Reply #9 on: 12 November 2019, 12:29:48 »


even though you flushed it in january, you can't rule out sediment of a 25 year old system being flushed from a rad and blocking the boiler ,say when some inpatient **** whacks the boiler up on a Friday after being away  ;D :D

Yes... regretting that now...  :-\

Let sleeping dogs lie and all that!  ;D
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Eboy.com

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Re: Boiler Short Cycling
« Reply #10 on: 12 November 2019, 18:17:18 »

Had this on my Potterton (Suprima).  In my case is was just the crap quality of the PCB, possible damaged in the early days due to the abysmal soldering on these Potterton PCBs.

As well as replace all the electrolytics, go over ever joint with a magnifier, and tart up and suspect joints.
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Kevin Wood

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Re: Boiler Short Cycling
« Reply #11 on: 12 November 2019, 21:06:57 »

I've probably got a load of the capacitors. Happy to swap them next time I'm over your way. :y

(can do am postal service on the spare board if it's urgent)

Is it lighting fully then shutting down fully (right back to fan off) or cycling through the ignition sequence (fan then pilot then main burner) with the fan running constantly?

I think the cap failure normally results in the latter. The former is likely to be the main thermostat, or maybe the overheat thermostat is tripping for some reason.

Ours kettled very badly when we first moved here and I found the system had been poorly maintained. Fixed a leak that was causing it to take on fresh water and gave it a good flush and some inhibitor it's been silent ever since.

They are worth persevering with. Fix the dodgy caps and lubricate the fan bearings every so often and they'll go on for ever.
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Sir Tigger QC

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Re: Boiler Short Cycling
« Reply #12 on: 13 November 2019, 00:33:33 »

Hi Kevin,

It shuts down completely including the fan and then goes through the ignition sequence from scratch, and as it gets hotter it'll run for less time before shutting down.

I had a quick peek in the F/E tank in the loft today and there's quite a lot of crud in there, so maybe it'd benefit from another flush.  I've got a box of Fernox DS40 (a citric acid cleaner) which I bought ages ago for it, but chickened out!   :D

Maybe I'll man up and give it a go!   :)  And I'll certainly take you up on your offer to sort out the capacitors thanks!  :y

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Fuse 19

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Re: Boiler Short Cycling
« Reply #13 on: 13 November 2019, 07:31:33 »

IF it is a gas related problem,like modulating gas valve bummed ,you should pay and have a "gas safe " engineer to rape you  ;D

Except they are of course NOT engineers, they are fitters (and hence why the items we talk about in this thread will be alien to them  ;D ;D ;D)

Profile is an on/off gas valve, no modulation, probably why they are so reliable ! ;D

And the cycling will have nothing to do with the kettling
« Last Edit: 13 November 2019, 07:42:29 by Fuse 19 »
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dave the builder

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Re: Boiler Short Cycling
« Reply #14 on: 13 November 2019, 10:22:24 »

IF it is a gas related problem,like modulating gas valve bummed ,you should pay and have a "gas safe " engineer to rape you  ;D

Except they are of course NOT engineers, they are fitters (and hence why the items we talk about in this thread will be alien to them  ;D ;D ;D)

Profile is an on/off gas valve, no modulation, probably why they are so reliable ! ;D

And the cycling will have nothing to do with the kettling

I agree in part about a gas safe engineer not being an engineer,  but some do have good knowledge and possibly engineering training, some are just plumbers who can solder a pipe but have no idea when it comes to the complex electrical systems of a modern boiler ,many just parts swap or replace the entire boiler  :(

I've watched a few gas "safe"  ::) plumbers on jobs and thought to myself  "not going to bother with leak detection spray for those connections you just had apart then Mr gas safe"  :-X
I said...
IF it is a gas related problem,like modulating gas valve bummed ,you should pay and have a "gas safe " engineer to rape you  ;D
purely because gas is not to be messed with if you don't know what your doing  :y
In the same way electricity is dangerous too, though most houses have RCD protection these days ....


then again, this is OOF , many here might still have gas lighting or a wylex rewirable fuse box at best  ;D :D

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