Just fitted a Worcester 40 cdi combi today and was doing usual installer checks for commisioning. Noticed that heating was still on even though room stat was off. Checked switched live on honeywell stat (240v) with neon tester and showed dead. Checked live return on boiler and again showed dead. So I tried testing with multimeter and was getting 24 volts returning from room stat to boiler. Turn up the boiler stat and the boiler fires up. Seems the boiler is responding with a return of 24 volts. Have Worcester got a problem as one of their engineers told me that early Ri models were experiencing problems when fitted in conjunction with Honeywell y-plans. It was too late to call Worcester as it was 6.30 and I was wondering if anybody else has had any similar problems.