My dhw gravity fed pumped heating system problem.

[IanCastleford]

Hi, i have an old gravity fed dhw with pumped heating system. My boiler is an old Baxi bermuda 552 with a honeywell st7100 programmer and salus room thermostat, no cylinder stat.

I'm not sure if this is ok but when i turn the central heating on regardless off whether the room stat is calling for heat, the boiler turns on. only when i turn the heating off at the programmer does it turn off. I thought that the room stat should control both the pump and boiler? At the moment the room stat is merely a switch for the pump, and so the boiler continues to cycle, heating the water. Now i know it's an old gravity system but surely when the room stat breaks the connection it should also turn the boiler off too?

I've checked the installation wiring for the programmer and it seems to be correct so i'm a bit baffled with it.

 

[kevplumb]

you can't have heating without water on a gravity system

so the stat controlling the pump is right

when your boiler fires its heating the water

 

[mikely]

The boiler will cycle on and off dependent only on its temperature setting. With a conventional gravity system the boiler is on all the time. You can improve the system by adding a tank thermostat and wiring it as shown in the diagram. When you are not using the heating, the hot water temperature will be controlled by the tank thermostat. When the heating is in use, the boiler will turn off with the room thermostat if the tank is up to temperature. With the heating running, the tank temperature will also depend on the boiler setting and how much the boiler is running.

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