In message , Set Square
writes
In an earlier contribution to this discussion,
logized wrote:

I am looking at replacing my Danfoss 3 way motorised valve as part of
a central heating re-fit.
I have changed the actuator a few times over the years, so I am now
looking to find a type that is known to be very reliable.
So far, I cannot find much independent info to help me decide on a
make. Drayton seem to make good TRVs, so are their motorised valves
as good? or maybe Myson or Honeywell, their specifications look good
also. Any ideas.

Dave

3-port mid-position valves have an inherent weakness in that they rely on
microswitches in the actuator to control both the valve and external parts
of the overall system - inluding switching boiler and pump on in CH-only
mode. It only needs a bit of wear on the cams which operate the
microswitches for the whole system to fail. Some makes may be marginally
better than others - but there ain't a lot in it.

I don't think I've ever come across cam wear in an actuator head in the
(high) hundreds which I've repaired in the past

The most common problem is synchron motor failure - they all use more or
less the same motor (although there were some better quality ones in the
past

The second most common fault is contacts burning on the microswitches
(again in the past some actuator heads used larger microswitches)

The other common problem is weak return springs
--
geoff