2x Potterton Suprima 70s lock-out

[hrg207]

I have 2 suprima 70 boilers serving the CH and water (megaflo) systems. PCBs (single light version) have been changed in both over the past 2 years, the system was a new build now 8 years old. Both boilers have started to lock-out (flashing red light) in the morning. They start immediately upon reset and run faultlessly for the rest of the day, next morning they are locked out. I have CH and hot water running, no funny noises or unusual symptoms although the radiators appear to be a lot hotter than before. I've searched the forums but can't find any circumstances where 2 boilers simultaneously lock-out so am assuming the fault likely lies outside of the boilers? Expect to have to call a professional in but would like to be as informed as possible as to likely causes before then. Would be grateful for any advice.

 

[glasgowgas]

if you have 2 boilers running independently of each other (1 doing ch only and 1 doing hot water only)

and both lockout at same time then it must be something they both share thats causing fault

incoming gas?

electricity supply?

 

[hrg207]

The boilers work collectively on the CH and hot water ie they share the load. I'm going to turn the CH off for tomorrow morning to see if the problem is coming from there.

 

[glasgowgas]

View media item 15765
if its any help

 

[hrg207]

Thanks Glasgowgas. Although I think these indicators are for one of the earlier PCB versions. Mine have only one light which changes between green and red depending on status. The lock-out is a 1 sec flashing red light.

 

[twgas]

I think it may be a faulty thermister on just one of the boilers, causing the system to get too hot and thus making both boilers going to overheat lockout.

 

[hrg207]

Thanks for the suggestion, would a faulty thermistor only cause a lock-out when the system started because the boilers behave themselves after I've reset them at the beginning of the day? I assume I could trace the faulty boiler by turning one off and seeing if the other one starts in the morning. Is a thermistor replacement easy to do?

 

[twgas]

Are you sure it's locking out first thing and not the night before but not noticed until the next morning?
or it might be lack of pump overrun/by-pass.

 

[hrg207]

Good point, I'll check tonight. Does the lack of pump overrun/by-pass signal a faulty pump? Thanks

 

[twgas]

Pump overrun is controlled by the board (pump supply taken from "pump live" on boiler connection block) on these, by-pass is something that should be fitted when boiler installed. If rads and water heating properly the pump is likely to be OK,

 

[Mr Smyth]

If they are the newer PCB then press the reset for >10 secs and count the flashes when you release. This will tell you whether it is ignition lockout or overheat.
Sorry, off the top of my head cannot remember which is which. Details are in the install manual for the new PCB.

Often the early morning lockout is ignition due to moisture on the electrode.

Needs to be checked by a GSE

 

[hrg207]

Thanks for the reply, would there have to be moisture on the electrodes of both boilers for them both to lock-out or would the failure of one make the other also lock-out?

 

[hrg207]

Well. both boilers locked out again this morning so not CH at fault. I did the test on the reset button, holding down for >10 secs, and got 5 flashes which according to my PCB manual indicates overheating. Going to switch one of the boilers off tonight and see what happens to the other one in the morning.

 

[heatingman]

I'd start by checking the by-pass is correctly set and if an automatic version that its not sticking.
Also with a twin suprima set up, how is the pump wired in? If its being controlled by a relay/timer is that functioning correctly.
You have managed to pin it down to an overheating problem, its now a case of checking for correct flow/circulation.
Are the boilers actually firing up in the morning and locking out (sticking pump) or shutting down on overheat last thing at night.

 

[hrg207]

Turned one of the boilers off last night, the remaining one was still working this morning and we had some heat and hot water. But now both the boilers are responding to demands for heat/HW, run for about 10 secs, make a noise like boiling kettle and then return to standby (green flashing light). The rads are cold and I assume the water isn't heating. Does this point to the pump being faulty?