understanding 3-port valves?

[Hunter72]

Hi All

I have a Potterton Suprima 50, installed with new build house since 2000, started to go into 'lock out' last week then eventually packed in all together. Took some advice from these forums and re-soldered all joints on the PCB, worked ok for a couple of days. Found out about the fiasco with 'Watchdog' on the BBC, called Potterton, there's an engineer popping out tomorrow (28/05/2007) free of charge to sort things out!

Anyway, I was intreagued to understand how my central heating works so I delved deeper into my system, I have the following:

Potterton Suprima 50
Sunvic Select 207 Programmer
Sunvic SD2701 3-port Unishare valve
Sunvic cylinder stat.
Drayton electronic room stat. (forget model but basically, 'ON' or 'OFF')
Sunvic WC 2202A junction box

I wanted to look into the wiring as I'm convinced the CH has always been on when the DHW was only needed (middle of summer and room stat not calling for heat).

I dug out the following drawing and checked it against my installation, it is wired exactly the same. I'm able to follow how the circuit works but can't understand how the room stat. demands heat from the boiler and pump.

My guess is that there are some clever bits of circuitry within the Sunvic SD2701 which involves a relay diverting power internally when the 'grey' wire becomes 'live'. When the 'grey' wire becomes 'live' a relay diverts 240 volts from the 'white' wire onto the 'orange' internally either when the cylinder stat. becomes 'satisfied' or 'HW OFF' is selected on the Programmer. This then allows a call from the room stat. to demand heat from the boiler and pump.

Hope this makes sense to someone?

I'm not a plumber but I'm curious to know how the circuit works.

Many thanks in advance for any shared knowledge.

DH

 

[dal5band]

All I know is that a 3 port valve is some clever piece of electrical balancing act that achives the flow to HW and CH sides acording to the demands of the relevant thermostats. The actuator has three positions - off (spring), mid-position and fully on - this is quite tricky to achive with the one motor. The mid-position is some sort of dynamic balance achieved by the motor and micro-switches so when it goes wrong it's difficult to see what's happening.

 

[Ethelred]

All 3 port valves work the same way.
When there is no power in the grey and white wires the valve is not energised and is for hot water only.
When there is power in the white wire a microswitch is energised and moves the valve to CH and Hot water.
When the white and grey wires are energised a microswitch is energised, 240v current is sent down the orange wire and the valve is moved to the cental heating only.
See the wiring diagram:
Central heating only;
CH on to 4, 4 to room statA, room stat calls for heat switch to B,B to 5 energises white wire. HWis off to 7, energises grey wire . Both white and grey are energised therefore 240v down orange to 8,9 &10 boiler fires pump runs. When room stat is satisfied no power to B no power to white therefore no power down orange therefore boiler and pump stop.
Hot Water only
HW on to 6, 6 to tank stat 1 demand, 1 to 8,9&10 boiler fires pump starts.
When satisfied stat goes to 2 current goes to 7 grey energised no power to boiler and pump. Central heating comes on power to white therefore power down orange boiler and pump start (power in white and grey) Then the hot water demands, no power in grey and orange but power to boiler and pump via 8. Power in white only puts valve in mid position

Cheers

 

[ChrisR]

All 3 port valves work the same way.

If only. Most do it's true, but there are quite a few variations now.

 

[Hunter72]

When the white and grey wires are energised a microswitch is energised, 240v current is sent down the orange wire and the valve is moved to the cental heating only.
Central heating only;
CH on to 4, 4 to room statA, room stat calls for heat switch to B,B to 5 energises white wire. HWis off to 7, energises grey wire . Both white and grey are energised therefore 240v down orange to 8,9 &10 boiler fires pump runs. When room stat is satisfied no power to B no power to white therefore no power down orange therefore boiler and pump stop.

Nice one Ethelred, you confirmed what I suspected and as dal5band said, clever bit of kit those 3-port valves.

The nice chap from Potterton arrived this morning to check things out. He changed the PCB and wiring harness (comes as complete unit). Took him about 25 minutes in all. Part number for the 'Replacement PCB Kit' is 5111603 for those who are interested or would find it useful.

In my original posting I mentioned suspecting the control wiring being incorrect as the CH and DHW have never operated independently. When the boiler 'played up' I took it upon myself to 're-wire' the control circuit to match the drawing linked to in my initial post. Now the repair has been carried out and with my 'new found' knowledge it turns out my suspicions were correct. DHW and CH can now operate totally independently or together as demand dictates so nearly eight years of wasting money!

Many thanks chaps, my knowledge has been enhanced, what a great tool diynot.com is.

Take care.

DH