Problem replacing old analogue room thermostat

[foxster]

I have an old dial Honeywell room thermostat and have purchased a Horstmann (model 099A) digital/battery programable room thermostat.
When I removed the old thermostat there were three wires: red, blue and yellow (NOT yellow/green).
The new thermostat instructions are very basic but seem to suggest a 2 wire instillation.
I wired up the new thermostat following a suggestion given to someone who posed a similar question on another site, i.e., red to NO terminal and yellow to Com terminal on the new thermostat and to disregard the blue completely. The thermostat itself could be heard 'switching' and the 'flame' icon came on to suggest it was seeking heat but the boiler did nothing.

I thought these were supposed to be simple to install - HELP!

 

[RF Lighting]

Which terminals were the wires connected to the old room stat?

If the wiring follows conventional colours then the new stat should work how you connected it up.

Does the new stat have a clock built in which needs setting?

Did you check the heating programmer was also switched on?

 

[Belle427]

you need to have a look at the boiler connections to see how its been wired