How do I wire UP a Honeywell 907 as old stat has 4 wires?

[Raybh]

My old stat is a late 1970s Honeywell which controls a 2 port Zone valve as I have a 2 zone heating system and hot water. There are 2 pairs of red/black wires connected to the 4 terminals numbered 2, 1, 4, 3. The first pair are black on 2, red on 1 and the second pair black on 4 red on 3. Both pairs show 230v when there is no demand and the bottom 4+3 show about 110v when heat is demanded. From other posts it sounds as though 1 is common, 2 is neutral , 3 is demand and 4 is satisfied. What goes where and what is redundant please?

 

[D_Hailsham]

My old stat is a late 1970s Honeywell which controls a 2 port Zone valve as I have a 2 zone heating system and hot water. There are 2 pairs of red/black wires connected to the 4 terminals numbered 2, 1, 4, 3. The first pair are black on 2, red on 1 and the second pair black on 4 red on 3. Both pairs show 230v when there is no demand and the bottom 4+3 show about 110v when heat is demanded. From other posts it sounds as though 1 is common, 2 is neutral , 3 is demand and 4 is satisfied. What goes where and what is redundant please?

I'll see if I can help, but I need more info about your system.

First of all, wire colours mean absolutely nothing in heating systems.

We need to find why there are connections to all four terminals, normally it is just three - satisfied is not connected.

Which zone valves do you have (make and model no)?

Are there any identifying numbers for the Honeywell stat?

 

[Raybh]

My old stat is a late 1970s Honeywell which controls a 2 port Zone valve as I have a 2 zone heating system and hot water. There are 2 pairs of red/black wires connected to the 4 terminals numbered 2, 1, 4, 3. The first pair are black on 2, red on 1 and the second pair black on 4 red on 3. Both pairs show 230v when there is no demand and the bottom 4+3 show about 110v when heat is demanded. From other posts it sounds as though 1 is common, 2 is neutral , 3 is demand and 4 is satisfied. What goes where and what is redundant please?

I'll see if I can help, but I need more info about your system.

First of all, wire colours mean absolutely nothing in heating systems.

We need to find why there are connections to all four terminals, normally it is just three - satisfied is not connected.

Which zone valves do you have (make and model no)?

Are there any identifying numbers for the Honeywell stat?

Thank you for the quick response. Originally the system had Sunvic MOMO valves on both zones and HW. Now I have the common Honeywell zone valves which have the open lever, synchronous motors and spring shut. I can't see the model nos and likewise with the thermostat as it has worn off with age!

 

[D_Hailsham]

Originally the system had Sunvic MOMO valves on both zones and HW.

That would explain why you have a wire connected to the SAT terminal.

Now I have the common Honeywell zone valves which have the open lever, synchronous motors and spring shut. I can't see the model nos and likewise with the thermostat as it has worn off with age!

You don't need the SAT connection on these valves. It should be disconnected at both ends and made safe.

Terminal 1 is normally Live, 2 = Neutral, 3= Call, 4 = Sat.

You can easily confirm this with a meter as follows:

The voltage between 1 and 2 should stay at 230V, for all positions of the stat.
The voltage between 2 and 3 should be 230V when the stat is turned to HIGH
The voltage between 2 and 4 should be 230V when the stat is turned to LOW

If this checks out, the terminal numbers are as above.

The new stat does not need a neutral connection, so this should also be disconnected at both ends and made safe.

Connect the new Stat as follows:

Live (wire originally to terminal 1) to A terminal
Call (wire originally to terminal 3) to B terminal

 

[Raybh]

Originally the system had Sunvic MOMO valves on both zones and HW.

That would explain why you have a wire connected to the SAT terminal.

Now I have the common Honeywell zone valves which have the open lever, synchronous motors and spring shut. I can't see the model nos and likewise with the thermostat as it has worn off with age!

You don't need the SAT connection on these valves. It should be disconnected at both ends and made safe.

Terminal 1 is normally Live, 2 = Neutral, 3= Call, 4 = Sat.

You can easily confirm this with a meter as follows:

The voltage between 1 and 2 should stay at 230V, for all positions of the stat.
The voltage between 2 and 3 should be 230V when the stat is turned to HIGH
The voltage between 2 and 4 should be 230V when the stat is turned to LOW

If this checks out, the terminal numbers are as above.

This checked out so I disconnected wires 2 and 4 and the stat still operated the valves and boiler.

The new stat does not need a neutral connection, so this should also be disconnected at both ends and made safe.

Connect the new Stat as follows:

Live (wire originally to terminal 1) to A terminal
Call (wire originally to terminal 3) to B terminal

Connected as above then programmed the stat and it works perfectly. I expect if a MoMo valve is fitted again then the wire to old 4 would go to new C. Thank you everso much.