If the boiler is firing up and you have the room stat and clock turned on, then its more than likely a problem with the diverter valve. What this looks like depends on the type of system installed. Its usually located after the pump, and if its a honeywell valve then it will have a silver coloured head. Here's a link to a picture of one, [url]http://www.plumbworld.co.uk/images/pwhv0012l.jpg[/url]. When in hot water only mode, the little lever you can see below the power cable will be stiff. When in heating or heating and hot water mode it will feel loose and slide from side to side quite easily. If its stiff and the heating is turned on then its more than likely the motor in the valve. It could well be the clock or the stat also but you'd need to get a multi-meter out and start fault finding, which is not advisable if your not a heating engineer. A quick fix if your desperate for heating is manually opening the valve. You can manually open it by dragging it across and locking it in position, if you take another look at the picture theres a little cutout where you can move the lever up and it will stay in the open postion. I hope this has helped. If you have any questions then leave a post and i'll try to answer them.
Neil (baxi engineer), August 2007
