Heating wont turn off


I've got a fully-pumped gas CH & HW system. My problem is that the boiler fires even when the control unit (timer) says that both the CH and Hot water are off. I don't have a separate frost thermostat (unless its built-in to the boiler - a British Gas "F2"). A British Gas engineer did call, and replaced a motorised valve motor, but that made no difference at all.
I was under the impression that the valve could not operate the boiler unless the timer was in the "on" position. The BGas engineer said that I was wrong (and he's the expect, not me) but if he's right, what is the point of the timer anyway ?
Any suggestions that don't include calling in British Gas would be greatly appreciated.
TIA,
Pete K
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Look at http://content.honeywell.com/uk/homes/systems.htm to check what sort of system you have. If it is an S plan then I would suggest a faulty valve not just a valve motor. Adam
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Adam,
Thanks for the tip, I'll have to study the diagrams and try to determine which one I have, but at first glance it is eother an "S" or a "Y".
Cheers,
Pete K
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.