Upstairs & water hot, downstairs not!

[Aberlee]

Hello, new to this, be gentle.
I've moved into a house with a problem with central heating.
When controller is switched to "Water Only" I get very hot water, but also, the radiators upstairs all come on as well.
When switched to "Water and Heating" All the radiators come on as you'd expect, but only downstairs appear to be controlled by the room thermostat.
I can't find any 3-way valves ( or any valves for that matter ) anyplace in the house and the boiler is an LPG fired "Ideal Mexico 2".
Does anyone have any ideas how I can just get hot water (in time for spring!) and how to bring my upstairs radiators under the control of the thermostat.
This couldn't have been done deliberately, could it
Thanks!

 

[chrishutt]

You probably have what is known as gravity circulation to the top radiators. The traditional remedy is to fit a check valve in the pipework so that no circulation can take place without the pump operating.

However you might want to consider upgrading the whole installation with pumped HW circuit, motorised valves, cylinder and room stats, TRVs, etc.