Too many zone valves

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hello
Hope someone can help! Fitting Hive thermostats to a large home which has a fully pumped system with dual zone central heating and hot water cylinder running off a Potterton gas boiler.
Confused by the three 2-port valves which are on the flow side of the system immediately after the pump. Please see picture. I can understand the two horizontal valves as being for upstairs and downstairs zones but can’t figure out the need for the vertical valve which feeds into the two horizontal valves. There is also a fourth 2-port valve (not shown on pic) on the feed into the hot water tank coil as expected, making a total of four 2-port valves! Any help / advice appreciated and apologies for the poor quality picture.
 
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A starting point might be to check which valves open and close with the existing prog and stats. On the honeywell valves when open the lever moves freely, closed resists movement.

I agree the valve before the T looks superfluous.
 
Agreed with above, in fact it looks like the pipe work around the extra valve has been modified as the insulation is different/missing.
That thermostat, what's it's purpose? Is it a main one or just in this room (garage?) Does it only go up to about 10c? Perhaps there used to be a frost radiator/loop on that valve which has been removed since.
 
I once came across an installation with an unexpected motorised valve where an old two port valve had been inserted to 'fix' a burst pipe. I realised when the cable wasn't connected to anything.

But as polesapart suggests all you can do is check its functionality and how it is wired in with the rest of the system. The insulation had been disturbed around the valve before the T, so possibily it was added later. Possibly it's been reconfigured to work as a single zone. But it's a bit of an odd way to do it.
 
Thanks all appreciate the comments.

polesapart - good idea, I'll check and report back when I'm next onsite.

John D - I hadn't thought of that but yes the insulation is different but nothing looks to have been touched for years. I'm guessing it could have originally been a single zone system upgraded to a multizone system. The thermostat in the picture is for frost protection as the boiler is in a garage.

stem - noted, system is definitely working as dual zone currently with two thermostats in the hallway and landing.

The bridged pipe below the vertical zone valve feeds the DHW coil (which has the fourth zone valve) and radiators in the main and ensuite bathrooms. This means that the bathroom / ensuite radiators are always on whilst the DHW is switched on. Would I be correct to assume these are also acting as the boiler bypass loop as I can't see any valves between the flow and return pipes close to the boiler?
 
I thought the thermostat was connected to that zone valve but I managed to zoom in and out isn't. So they are probably not related.
 
The vertical zone valve could be wired to turn off CH demand to the two zones from a standard two channel programmer (HW + CH) - this way would leave the the upper two zone valves independently controlled via separate upstairs and downstairs stats.
 
Mr Therm, thanks - the current thermostats are wired to the Live motor feeds of their respective zone valves (upper two zone valves), will check when I'm next on site how the vertical valve is triggered.
I didn't get a chance to properly check how the programmer is wired but it had one cable off the DHW NO terminal and two cables coming off the CH NO terminal.
 
It would be an odd way of doing it. Normally where two zones are controlled by one output from a programmer. The CH 'on' wire would go to both room thermostats which in turn would control a valve each. Job done. No need for a third valve.

Then there's the matter of how the microswitches inside the motorised valves would control the boiler. If the microswitch in the first valve was used, the boiler would fire up whenever the programmer was 'on' even if both room thermostats were satisfied. Not ideal! The two zone valves could be wired in parallel, and then as a pair be in series with the first valve of course, but why would you go to all of the effort and expense to add a completely unnecessary valve and complicate the wiring just for the sake of it :confused:

I will be interested to see the outcome of this one.
 
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Further update.
The vertical zone valve has the motor wired to Neutral and its Live terminal connected to the orange of the other two zone valves. So basically it opens at the same time as either of the two horizontal valves. Even more confusingly the grey and orange wires have been cut off so the switch part of the valve isn’t used. Zoom in to the mid-right of the pattress box to see cut wires on second image.
All I can deduce is that as ‘poles apart’ originally stated the vertical zone valve is superfluous and could be a remnant if an earlier layout that was changed to a dual zone system - badly!
I also found that the 4th zone valve on the DHW circuit has had it’s motor cable cut and switch shorted out. See first image. Basically a bodged temporary repair requiring the valve to be left latched open.

Hive installed and fully working for now. Thanks for everyone’s input.
 
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