SUNVIC SD2701 motorised valve/port valve?

My sister has one of these valves on her central heating system. Firstly is it a 3 way valve or is it a 2 port valve as I think it is the latter.The problem is that her central heating comes on when the room stat is off.I have taken the actuator head off and it clicks round when room stat turned up so seems to be working.The body part of the valve also seems ok as thevalve turns freely.Is it possible for the for the valve not to sit properly in the body.Also is it a motorised valve that gives either hot water only or central heating only or can both be on at the same time.If it is faulty what is the best replacement.

thanks

mark

Generally the sm prefix is mid position, sz is zone valve (2 port) and sd is diverter (3 port but no mid position)....how many pipes go to the brass valve under the actuator?...generally a passing valve will require a replacement valve body.

duplicate

It has the feed into the valve from the pump and then straight into the cylinder and another pipe going to the central heating,so by what you are saying you either have the water on and the central heating off or vice versa. I presume that is why on the clock it has either water priority or heating priority

No, the actuator head can't sit in the wrongh position

It could be a microswitch in the actuator head which has welded itself in the normally open position