Potterton Suprima 80L - problem? (not lock-out)

[carrotman]

Hi,

I have a Suprima 80L boiler running an open vented heating system and indirect hot water tank.

I'm not convinced that the boiler is working correctly though, seeing all the Suprima PCB stories on here - but I don't have the lock-out problem (yet?)

The boiler gets to temperature (red LED on, green LED flashing) but when the red LED goes out and the green LED keeps flashing, indicating a call for heat, the boiler does nothing for about 3 minutes. After the 3 mins it fires, heats, and waits again. This sequence repeats with more time spent waiting than heating.

The flow pipes get hot then cool, then hot, then cool etc as this goes on so the rads never really get hot.

Is this behavior a fault with the boiler (or something else), or is it normal? Surely the bolier should fire as soon as the call for heat is there.

Cheers

 

[gazthepottertonengineer]

could be your temperature thermistor or could even be down to poor circulation check your pump

 

[kevplumb]

ahhhh go on gaz tell him its the pcb

 

[carrotman]

thanks gaz - is there an easy way of checking the thermistor?

 

[geoff@cetltd]

It should be about 100kohms at room temp

I forget what it should be at operasting temp, I can look tomorrow

It's not a common pcb problem, so it's most likely the thermistor or a blockage / pump problem - heat not being removed from the heat exchanger quickly enough

 

[carrotman]

the thermistor appears to be functioning and there appears to be good circulation.

One thing I have observed whilst measuring the thermistor resistance:

if I power cycle the boiler when it's either in the "at temperature" (red on, green flashing) state or "call for heat" (red off, green flashing) state, the boiler fires straight away.

if I leave the boiler powered, it waits a few mins before firing.

to me this seems like more of a controler fault than a sensor fault - but I'm no expert!

 

[geoff@cetltd]

Oops, factor of ten out

1 mgeohm at room temp
about 73kohms at 82 C

 

[carrotman]

thanks raden - does this observation point to anything?

if I power cycle the boiler when it's either in the "at temperature" (red on, green flashing) state or "call for heat" (red off, green flashing) state, the boiler fires straight away.

if I leave the boiler powered, it waits a few mins before firing.

 

[Soggy_weetabix]

there is a built in delay to stop boiler firing immediately when a call for heat, on the suprima pcb.

Anti cycling measure apparently.

My advise would be be to save up for a decent boiler and drop your potty from a great height. They work fantastic as long as no gas or water are passing through them.

David

 

[geoff@cetltd]

thanks raden - does this observation point to anything?

if I power cycle the boiler when it's either in the "at temperature" (red on, green flashing) state or "call for heat" (red off, green flashing) state, the boiler fires straight away.

if I leave the boiler powered, it waits a few mins before firing.

yes, I went through that procesure today just to make sure

On start up the boiler runs straight through it's sequence without appreciable delay. Once it has reached temperature and switches off, there is a delay of several minutes before it goes thjrough the sequence again

 

[carrotman]

thanks all - going to get someone around to have a look.

 

[HarrogateGas]

Sounds just like the anti cycle is working normally to me.

 

[dublingas]

Hi Carrotman

did you manage to sort this one out I have an identical problem.


Brendan

 

[nickso]

suprimas have a terrible anti cycle on them......you can wait lonegr than 3 mins sometimes. switch it off and on again at the mains if you think its in anti cycle

 

[carrotman]

after some investigation there was a problem with the hot water pipe configuration. This fixed the problem with the hot water and appeared to fix the heating issue before the summer, but now it seems to be back - not all the rads getting hot despite attempts to balance. Think it's a combination of the suprima's "feature" and possibly sludge in the system, so will be considering another powerflush - or moving!