Replacing a Honeywell 3-port valve

[Skylark NW]

House was built in 1987 and still has the originally installed conventional boiler and central heating system. A good few years ago I replaced the electrical half of the Honeywell 3-position valve. I now have the same symptoms and think it appropriate to replace the complete valve.

Cold water tank in loft. HW tank, pump, 3-position valve located on first floor.

The FAQs say that the system needs to be drained down. Does this mean turning off the incoming main water stop cock and drain both the HW tank and the central heating radiators?

Many thanks.

 

[CBW]

No, it’ll refer to the heating circuit only. You can either use the stopcock or the isolation valve (if fitted) to the cold water storage cistern. There’s a method of bunging too, but if you prefer to drain,you only need to do below the level of the valve, no the whole system

 

[terryplumb]

Draining the central heating system at least to a point lower than the mid position valve would be necessary. Before you do that ,check the feed and expansion tank (f&e)for cleanliness. You do not want any gunk that is in the f&e to get into the system.
The hot water cylinder does not need to be drained.