Potterton suprima constantly firing up

[charmOl]

I have a potterton suprima 40 which constantly fires up every few minutes. It flashes green for 2 minutes, flashes red and green for 10 seconds then fires up. The boiler stays on for a couple of minutes then the process starts again.
I have hot water and heating so could this be a faulty boiler stat. The PCB was replaced about 15 years ago, the boiler is 20 years old.
Thanks.

 

[CBW]

Greetings,

Just FYI, this would have been better in the plumbing/heating sub-forum, mods may move it.

Have you checked the motorised valve(s).

 

[charmOl]

Thanks for the reply. Yes, sorry but didn’t realise as I’ve just joined the forum and it’s my first post.

I’ve pulled the lever over on the 3 port valve and it moves back, so I think it’s working ok.

 

[charmOl]

I have a potterton suprima 40 which constantly fires up every few minutes. It flashes green for 2 minutes, flashes red and green for 10 seconds then fires up. The boiler stays on for a couple of minutes then the process starts again.
I have hot water and heating so could this be a faulty boiler stat. The PCB was replaced about 15 years ago, the boiler is 20 years old.
Thanks.

Read more: https://www.diynot.com/diy/threads/potterton-suprima-constantly-firing-up.585860/#ixzz7JUIqrdyn

 

[CBW]

Ah, no bother, I’ve reported it, so hopefully mods will move it, and if I’m wrong with my diagnosis, then more experienced can reply.

Unfortunately, that testing doesn’t prove much, other than it springs back. It might be a stuck microswitch.

 

[charmOl]

Thanks for the advice CBW, re posted on the plumbing/heating forum.

 

[charmOl]

How would I test the microswitch or should I just replace the head.

 

[CBW]

With no demand test between the orange wire with neutral or earth, if it’s 230vac, then you’ve probably got a stuck microswitch.

 

[charmOl]

Cheers CBW, I’ll check it in the morning. once again thanks for your help.

 

[BlueLoo]

"Can i just add that talking in grey is a brilliant way of having a "Ghost" convo. Never thought of that before and i am worldly web wise..."

 

[charmOl]

Just realised I only get this problem when I put the c/h on. As soon as I stop demand for heat the boiler works ok.

 

[CBW]

Just realised I only get this problem when I put the c/h on. As soon as I stop demand for heat the boiler works ok.

Just so I understand this correctly?

Heating on - boiler ok
Hot water only - boiler ok
Both together - boiler fires up constantly

 

[charmOl]

Heating only-constantly fires up
Heating/hot water-constantly fires up
Hot water only runs normal.
Could it be the programmer?

 

[CBW]

Could it be the programmer?

Highly doubt it. Sounds like a stuck microswitch. On a 3 port mid position valve, the hot water isn’t activated by a microswitch, whereas heating only/both together use a microswitch.

 

[jackthom]

Sorry @charmOl I’m not clear whether the problem is the boiler coming on when it shouldn’t be on, or whether you are concerned about the boiler cycling.

When you say Heating ON do you mean On at the programmer but turned Off at the room thermostat, in which case I’m with CBW on this one.