The post is partly as a reminder to myself, and partly for anyone else who finds themselves with the same requirement.
On the boiler primary circuit for my new solar cylinder there’s a Honeywell V4043 2-port zone valve. This particular model is a H1056 which has 22mm compression fittings and a SPST (single pole, single throw) auxiliary switch. I need this switch to control the DHW suppression on my Viessmann Vitodens 100 boiler (I’ll elaborate on that another day), but the circuit has to be active when the 2-port is closed whereas the zone valve only has a wires for the common (C) and normally open (N/O) poles on the switch.
I looked into whether I could get a Honeywell zone valve with a head having a SPDT (dual throw) switch which I could exchange for the one already plumbed in – they do two (the H1106 and H1080) but ~£70 this looked an expensive, and wasteful, option.
UK domestic 2-port zone valves have standard wire colours:
- brown, blue and green/yellow: used to energise the motor and open the valve
- on models with an auxiliary switch (SPST or SPDT):
- orange = common
- grey = N/O (i.e. connected to common when valve energised and fully open)
- (SPDT only) white = N/C (i.e. connected to common when valve closed)
So my SPST valve only had an orange and a grey wire for the aux switch. I then took the head off the valve, and removed the motor, to see if there was any way to re-wire or replace the microswitch.
The microswitch (on the left in the picture) was Honeywell branded but does have odd terminals rather than the more usual spade connectors.
I’d read about zone valve motors and, sometimes, microswitches needing to be replaced so searched to see if I could get a SPDT replacement (e.g. at RS and Farnell) but couldn’t find one with these terminals.
On closer inspection I could see that actually it already was a SPDT type, including a small hole for the N/C connection, but it was a sealed unit and the wires were firmly attached (soldered I assumed).
You can just see from the outline that this is a fairly typical shaped V3 microswitch but with an extra bit of casing around the terminals.
On the reverse there’s a small plastic rivet (about 2mm across) which holds the case together.
I sliced the top off this and prised the case apart, being careful not to disturb all the springy bits inside! I could see that the wires just had tinned ends and were pushed into the connector.
By gently pushing the connector spring away from the wire I could release it, allowing it to be removed from the N/O terminal and then pushed into the N/C one.
With hindsight I could have saved opening the case by cutting the grey wire off very close to the terminal, tinning it again and pushing it into the N/O hole.
Finally, I replaced the cover and put a little epoxy glue on the top of the rivet (though the microswitch is screwed to the valve so that would hold it closed anyway) prior to reassembly of the valve head.
Note I’ve put a piece of white insulation tape on both ends of the grey wire to hopefully make it clear this is not a regular aux. switch in case it ever needs replacing (and will include it in the central heating documentation).
So now this valve can do what I need, and in doing so will save a small power supply and relay (that’s the ‘green’ link I suppose!) – more importantly it makes the system simpler and with slightly fewer parts to go wrong.
More on the central heating system design to come… we’ve no heating yet so blogging is not a priority!
