My mother-in-law's central heating system has a problem. When HW only
is selected, the hot water is heated and the central heating is off.
However, when we select CH only, the CH heats up but so does the HW.
By the hot water cylinder and pump is what I assume to be a Mid-
Position Three Port Valve. The motor unit (Honeywell 40003916-003) was
recently replaced by a plumber (to fix the opposite problem whereby CH
came on when HW was selected).
I believe the plumber to be competent but he appears not to know what
is wrong. Please can anyone suggest what the problem is?
- posted 12 years ago