Potterton CF100 Coming on at random

[Axel]

My Potterton CF100 used to have only one live connection as it was on a previous gravity circuit, so it only came on when told to by one of the stats, via a one of the motorised valves. Now that it is on a sealed system with pump overrun, it has a permanent live and a switched live connection.

The problem is that it occasionally fires up at random, even though there is no call for heat from any stat. I have yet to check the motorised valve microswitches, but I suspect it is the boiler itself coming on for some reason best known to itself. There is no frost stat, and in any case, it's not particularly frosty at the moment!

Has anyone seen this fault on this model before?

 

[twgas]

which potterton 100cf do you have?

 

[Heating one2one LIVE]

Other than the zone valve head powering itself as you mentioned already,if the zone valves are wired into a "Honeywell Sundial"wiring center then I would suspect that(If theres power to the switch live when the boiler's coming on without a demand that is).

 

[Agile]

The Potty CF100 is a pretty old floor standing boiler with cast iron heat exchanger.

I was not aware that they could be converted for a sealed system.

Are you quite sure that it can be converted and has been by a competent person?

Tony

 

[Axel]

Thanks for your concern Tony - yes, I followed the MIs to the letter. It's the CF version of a Kingfisher MF 100BTU/hr. Says sealed system is ok if done according to blah blah.

Just wondered if anyone seen a PCB fault manifest itself in this manner?

 

[Agile]

Right! Its a Kingfisher MF !

Thats a reasonably modern boiler and of course can be configured for a sealed system.

The original CF100 was suitably inefficient to be included on the scrappage list !

Tony

 

[Axel]

Ok, sorry Tony, my fault for being inaccurate in my OP!

Still has the intermittent problem though....

 

[Agile]

A simple test you can do is to wire a low power mains bulb between SWL and neutral so that any signal from the controls is then proved visually when it fires up unexpectedly.

Of course you do need to be there to see it.

Or alternatively to have a security camera watching which is fitted with a video motion detector so that it will record just when the light comes on!

Tony

 

[Axel]

Yes, I thought of that already, but if there was a PCB fault leading to a backfeed of live from permanent live to switched live during the fault condition, then such a home made indicator light would not show if the erronous sw live was coming from outside of the boiler or the pcb itself.

i might rather fit a light switch inseries with the SW live connection so that if I witness the boiler doing an unauthorized light up, then I can switch off the switch and see what happens.

I suspect a PCB fault as it is only now that I am using a separate SW live connection that it is doing this.

 

[Agile]

I am sorry you dont want to folow my suggestion.

In that case just disconnect the wire from your SWL and you are likely to be proved wrong as I am expecting that it will probably not come on at all in that case.

If it does then it will not be as a result of anything feeding any live to the SWL but as a result of the PCB producing another internal fault condition.

But do something!

Tony

 

[Axel]

As I explained, I shall leave the SW Live connected, but via a lightswitch that will be left in the closed (on) position. If I then ever see the boiler firing when all the stats are off, only then I will turn off the switch to see if that makes the boiler go off at the same time, which would prove if it was an external SW live that was making it fire, rather than an internal PCB fault.

The SW live connection on the boiler, if not operating a relay on the pcb, might be an electronic trigger, which might be susceptible to stray AC picked up from the cabling if it is a high impedance input. A switch near the boiler would isolate that also.

Maybe someone out there has knowledge of the electroonics used on that pcb.

Might just take it to Adlink for a refurb....

 

[corgiman]

if its the MF (which as tony says is not that old a boiler) its probably the potentiometer that has gone (boiler stat)

had a few of these go which results in the boiler coing on when the stat is turned off.

 

[Axel]

had a few of these go which results in the boiler coming on when the STAT is turned off.

Thanks...the word STAT that I have capitalised - are you referring to the external room / cylinder stat, or the boiler stat itself. i know that the potentiometer is the stat in the boiler, but which stat is it you refer to in the latter part of the sentence?

 

[Agile]

He means the potentiometer on the boiler which controls the set temperature.

You can test it by disconnecting from PCB and measuring from slider to each end of the track as you slowly turn it from end to end and watch the resistance vary.

I am sorry that you would even consider taking any PCB to Adlink!

Tony

 

[Axel]

Hmm...The pot generally works as it controls the boiler temperature correctly.

Tony, are you concerned about safety or quality issues with an Adlink board? It's for my own boiler, not a client. I would be wary of using them on a modern boiler pcb, but this one is quite a basic traditional electronic board. A one year guarantee on it should be reassurance to give the board enough of a go to test if it's a good one.