My father, DIY "genius" that he is, was having some trouble with his central heating system and was told by the service engineer that the problem was the head on one of the 2-port valves.
Anyway, turned out the next door neighbour had a spare motorised valve head from when he had his sytem altered and it happened to be the same make (Danfoss). However, when I examined what my father had done it turned out the head he was given was for a 3-port valve sytem, which he's fitted onto the 2-port valve body.
Apparently the cable colours are all the same so he's just wired it up the same way. The valve is on the hot-water side of things, so has anybody got any ideas what i liable to happen when he goes to turn the heating back on?
The spigot on the body is different on the two types, one has a I shaped peg, the other is rectangular. They are not directly interchangable, but parts may be swappable.
I found the 3 port ones unreliable, I had to change the micro switches regularly.
Assuming that it will fit physically, the electrics are totally different. A
2 port-valve is either open or closed. A 3-port valve can be half-way open (mid position). But probably the biggest difference is that a 2-port actuator has 2 wires for the motor, and 3 totally separate wires connected to a switch which toggles when the valve is open - and which is used in an S-Plan system to switch on the boiler and pump. A 3-port actuator *doesn't* have separate circuits - they're all mixed in together. So you'll get very peculiar results. When I get time, I may look in more detail as to actually what will happen. But you're likely either to end up with the boiler not on when it should be - or on when it shouldn't be. It may not actually do anything dangerous - just undesirable!
Having looked into this a bit further, my considered opinion is as follows:
3-port valves come in 2 flavours - diverter valves, and mid-position valves. A diverter valve is relatively simply, having only 2 positions. The incoming water is directed either to the HW circuit or to the CH circuit - but never to both at the same time. Some valves have secondary contacts which switch when the valve moves from HW to CH. If the 3-port actuator in question had identical wiring colours to the 2-port one which it replaced, the chances are that it came off a diverter valve rather than off a mid-position valve. If this is the case, it has a very good chance of working satisfactorily.
An actuator for a mid-position valve does *not* have exactly the same wiring colours as that for a 2-port valve. In addition to orange, grey and blue, it has a single brown/white wire rather than separate brown and white wires. Assuming that this is connected in place of the 2-port valve's brown wire, the following will happen:
When hot water is demanded by the programmer and cylinder stat, the valve will start to open. When it gets to the half-way stage, the first micro-switch will throw - connecting the motor to permanent live on the grey wire. This will cause the valve to continue to open - and it will remain fully open for ever thereafter. The second micro-switch will also throw (just after the half-way point) and will connect the HW demand to Orange - causing the boiler to fire, and the pump to run.
When only HW is required, the system will work ok - with the boiler and pump going on and off according to the demand. However, whenever the boiler and pump are turned on in response to a CH demand, the HW will get hotter and hotter (to approaching boiler temp) even though its demand is satisfied - because the HW zone valve is *always* open regardless.
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