How is my back boiler's hot water circulated?

[Brouhahaha]

Hi,

I'm not in my (second hand) house all that long and am trying to figure out the plumbing. The range has a back boiler and when lit it heats two radiators up stairs and the hot water tank also up stairs. To my knowlege there's no pump running so how does it circulate the water? Or is there perhaps a pump somewhere that "kicks in"?

There is a pump in the hot press that doesn't seem to do anything and a switch on the wall of the hot press whose function I don't know. Is it possible this pump should be operational but isn't and despite that some of the heated water is moving up the system?

If the range is particularly hot I can hear what I think is the back boiler's tank "hopping" as if the water has reach a v. high temp. Bit disconcerting when I'm not certain the system is as it should be...

TIA

 

[Hoagy]

The water is circulating by gravity which is the way it must be done with solid fuel.
Noises in the back boiler mean the water is starting to boil, it also may start pitching from the expansion pipe into the header tank in the attic.
You can usually relieve that by running the hot water tap. It sounds worse than it is, but it's not ideal.
You don't mention any downstairs radiators, which would probably be the purpose of the pump. The pump may be kaput or just stuck, there's usually a removable cap in the centre of the housing which gives you access to the shaft so you can free it up with a screwdriver.

 

[ted]

I had a similar system - fireplace back boiler and the switch and pump in the hot press. Check if the wiring from the switch goes to the pump. I also had a thermostat on the pipe in the hotpress linked to the pump.

My switch was to override the thermostat and manually switch on the pump. But as Hoagy said it would circulate by gravity.

 

[Carpenter]

Sounds like your pump is not working; your back boiler is still heating the rads through gravity circulation, but this is not safe, there is a risk of damage to the back boiler if the pump is not in action. Have the pump checked out by a plumber and see what controls (if any) may be added to improve the operation of this system.