I'm having a problem (I think) with a BB 401 Back Boiler; the system is fully pumped with cylinder/tank & room stats and a 3-way valve. A faulty boiler pilot light thermocouple has just been replaced and all appeared well; however I'm recently finding that, when the room (or tank) stat is calling for heat the boiler will light up for a reasonable while, then shut off briefly (30 seconds or so) then light up again for a brief period (50 secs) and so on. At all times when this is happening the room (or tank) stat is always calling for heat - it's not switching off/on/off etc.
It seems that, even when the room (or tank) stat is calling for heat, the boiler stat beneath the gas fire is controlling the burner - you can hear it clicking off/on etc. in synchrony with the burner flame. Winding the boiler stat up to a higher setting initially causes the burner to immediately light up again and burn for a longer period before commencing the off/on/off cycle, but then the same process kicks in again - albeit at a higher boiler/heat exchanger temperature. The boiler stat is currently at position 4 (one step away from it's highest setting) as I type this, and the burner is cycling off/on/off at regular intervals.
The pump shaft is nice and free to turn and self-starts straight away when demanded; the pump speed setting switch (I never knew it had one) was on position 2 - it's now on position 3. The 3-way valve plays nicely and the hot water and all rads warm up quickly; room & tank stats control the system correctly. There's no unusual noises, signs of airlocks etc.
I've not noticed this behaviour before, so something's changed/not right....
Any ideas please - the pump has been suggested, however all upstairs/downstairs rads (4) are getting nice n' hot?
polybear
It seems that, even when the room (or tank) stat is calling for heat, the boiler stat beneath the gas fire is controlling the burner - you can hear it clicking off/on etc. in synchrony with the burner flame. Winding the boiler stat up to a higher setting initially causes the burner to immediately light up again and burn for a longer period before commencing the off/on/off cycle, but then the same process kicks in again - albeit at a higher boiler/heat exchanger temperature. The boiler stat is currently at position 4 (one step away from it's highest setting) as I type this, and the burner is cycling off/on/off at regular intervals.
The pump shaft is nice and free to turn and self-starts straight away when demanded; the pump speed setting switch (I never knew it had one) was on position 2 - it's now on position 3. The 3-way valve plays nicely and the hot water and all rads warm up quickly; room & tank stats control the system correctly. There's no unusual noises, signs of airlocks etc.
I've not noticed this behaviour before, so something's changed/not right....
Any ideas please - the pump has been suggested, however all upstairs/downstairs rads (4) are getting nice n' hot?
polybear
