F&E tank overflowing. why ? Oh why ?

[Gasguru]

Er not quite...we're are talking about gravity circulation through the cylinder primaries.
Circulation of boiler water to the cylinder coil (often a single coil) via 28mm pipework.
Many installations barely work due to the head/horizontal distance from back boiler to cylinder.
Boiler fires up...boiler stat turns off...heat exchanger losses heat via flue and repeat.
Gradually water circulates up and around coil.
Maybe 50% efficiency at best.
Concept fine when coal and gas were really cheap.

 

[bernardgreen]

OK I was mixing up this thread and solid fuel back boilers where failure of the electricity supply creates a hazard of the boiler creating steam if the fire is not extinquished in time

 

[Nige F]

I've often wondered if an annulus was more efficient, as fitted to old gravity primary cylinders, rather than a coil. I know that when converted to fully pumped they needed to flow from bottom to top or you'd get noise from the water/air trapped in the top. Or maybe I just like the word annulus.

 

[David cooper]

Update, problem solved !
I replaced the gas valve & set the burner pressure to 10 m/b (old one was set at 14 m/b.
Now everything is behaving great. ( customer phoned me 3 days after to confirm)
Thinking about this, I reckon that although everything is behaving, there must be a partial blockage somewhere in the system & reducing the burner pressure just means that it's not under as much stress now.
Thanks for all the advice.