Help!

[big al]

Helped my neighbour replace an old single rad(approx 30yrs old) for a new double rad, had to alter old pipework to fit new valves. So drained down the sysyem, altered pipe to suit new rad refilled the system and bled the rads. Switched on heating all come on fine and went off ok, but when the water gets heated the rads upstairs come on???????

What is the cause and how do i fix it please.

what type off system is it ?
has it always been doing it ?

[big al]

not too sure on the type of system, cant find a diverter valve in the airing cupboard, and it never used to do it before

if its a gravity hw, pumped heating system.
sounds like the gravity check valve is stuck open.

[big al]

ok thanks

[big al]

finally got round to changing the gravity check valve, but the rads still come on upstairs when the hot water heats up....????