gloworm fuelsaver 50ff

[ScottishGasMan]

Hey all, very stuck at this one

was at it the other day, boiler was needing a new aps, so i ordered one and stuck it in the next day, boiler fired up 1st time fine, let it run for five min, then left.

Boiler came back in yestarday, since id been they hadnt had any hot water or heating, everything was luke warm.

I tested it, and suspected the thermostat to be "gubbed" it fires fine heats ok, bur only heats for a few mins, once the flow pipes hot it cuts off, then the flow pipe cools within maybe 30-60 seconds, but the boiler doesnt come back on for 10-15min so never gets any real heat.

anyone got ideas, im totaly stumpped, (oh and tryed a spare PCB in it, still the same)

Cheers Guys
SGM

 

[gas4you]

I think these have one of these very basic thermostatically controlled pump overrun stats. Check this out. A fairly common problem on these.

 

[ScottishGasMan]

sorry, I totaly didnt realize what Id written, changed the thermostat today before the PCB.

 

[gas4you]

Have you checked external zone valves and pump etc. Sorry not trying to teach you to suck eggs

 

[ScottishGasMan]

lol, no I need to stand back and look at the bigger picture. theres no zone valves, they just turn the rads off at the valves, fully pumped. pumps an old grundfoss, seems to be moving the heat the boiler does make out fast eoungh.

I thought it could be sludge(there will be some in it there old systems) but the fact that teh moment the boiler cuts out you can feel the flow cooling from the cold return water comming in. so it feels to be flowing water fine, or at least enough.

If the boiler didnt go off for 10-15 min between firing it could heat the system fine.

when it cuts off the thermostat will go open circuit, then after maybe 50sec go short circuit, then nothing happens until 10 min or so later the fan comes on and the boiler fires up, which is why i was suspecting the pcb but its not that

 

[ollski]

The fan isn't slowing / sticking when it gets hot is it?

 

[ScottishGasMan]

thats a very good suggestion, never thought of that, but now I do, i dont think its that, something to keep in mind tho.

when the fan goes off it goes straight off as if the powers gone to it, there no slowing/grinding before it goes.