hot water cylinder

[chris35]

i have recently replaced my hot water cylinder with a similar 'hercal' indirect cylinder, but it doesnt heat up the water. i have checked the wiring which seems ok. i normally kept my hot water constantly on, via a switch on the central heating box on the wall in my lounge. by doing this the upstairs radiators stayed warm. oddly enough, the radiators are still warm even though the new tank is cold. 

[secretspirit]

Have you checked that the thermostat on the cylinder isn't set too low? If it's connected to a gas boiler then perhaps there is a problem with that.