Honeywell Powerhead problem

[Charles Victor]

My central heating has two, 2 port valves; one for the HW and one for the CH itself. The powerhead on the HW 2 port valve is a Honeywell 40003916 that failed and on which I have fitted a replacement.

The problem I now have is that the boiler only fires if the CH or CH and HW both demand heating. If the HW alone demands heating the powerhead operates (lever moves to full deflection) and the pump runs but the boiler doesn't fire. If I then demand CH with HW already demanded the boiler still doesn't fire. If I now switch off both HW and CH before then demanding CH only, the boiler fires. If I now demand HW with the CH already running, I get HW.

Clearly I have run one or more wires incorrectly on the HW powerhead but I cannot fathom how.

Guidance will be very much appreciated, thank you.

 

[Echo the husky]

Can you post some photos of your wiring? If there is a white wire on the new valve it needs to be safely capped. An S plan system is very simple, have you tried matching the wiring with a diagram?

 

[Charles Victor]

Thank you, Echo the husky. I am currently out of the house but will take and post a photo this evening.

 

[oilhead]

Pump and boiler are usually fired from the same terminal, or at least an adjacent one commoned up. This must be where your fault lies, as if it were a bad connection of the live feed or the cylinder stat, the pump would not run.

 

[Charles Victor]

Thank you each for the continued assistance. I am back home a little earlier than expected so have just taken the embedded photo as promised. Note that although the installation is a pig's ear compared to how I would have done it (and it wouldn't be on the floor underneath a web of plumbing and adjacent to the base of 300+ litres of Heatrae Sadia HW tank, either), the cable clamp is removed only because I have tried to position the cables for maximum traceability of the wire runs in the picture. From left to right, the four cables entering the junction box at the bottom of the image are as follows:

Black - CH 2 way valve
Black - HW 2 way valve (the valve I have replaced)
White - HW Thermostat
White - Pump

Admission: I was able to conscientiously and undisturbed connect the new powerhead, new wire for old wire, one at a time, apart from the orange wire running to terminal 13. I got disturbed by a long phone call and returned several hours later. When I did return I could not remember whether all four loose wires had been in terminal 13 or whether some had been in terminal 13 and some in 12 - which also had an undone screw. I was reasonably certain that 12 had been unused beforehand so reconnected all to 13 even though it was a cram to do so - as you can see. If it turns out I am correct to connect all four wires I will split the four wires in to two pairs in 14 and 15 with a bridging wire to join them but that's for a later moment when my problem is solved!

CH HW Junction Box

• Charles Victor
• 14 Jan 2018

 

[steve32]

How many wires are in number 8

 

[Charles Victor]

Two. The brown from the HW powerhead and a brown to the HW thermostat that can just be traced in the image; it runs parallel to and just below the brown from the HW powerhead before branching off to the right.

 

[Echo the husky]

The wiring looks like it should work. Check the connections carefully, especially terminal 13, beyond that you will need to take some voltage measurements. Does the pump run when only CH is on?

 

[Charles Victor]

Many thanks. I've remade each connection several times already so if you will please be kind enough to tell me what terminals to measure (I have a voltmeter) in which combinations of HW, CH and both, I will do so. Yes, the pump runs when only CH is on, as does the boiler; the CH powerhead moves too and the rads get hot.

 

[Echo the husky]

Measure voltage from neutral to:
11 240V all the time.
3 240V when CH is switched on at programmer
2 240V when CH on at programmer and room stat calling.
when 2 live, CH valve should open and 13 should have 240V on it (and boiler and pump should run)
10 240V when HW is on at programmer
8 240V when HW is on at programmer and cylinder stat calling.
when 8 live, HW valve should open and 13 should have 240V on it (and boiler and pump should run)

so CH only
240V on : 2,3,11,13

HW only
240V on : 8,10,11,13

CH&HW
240V on : 2,3,8,10,11,13

 

[Charles Victor]

Thank you very much indeed for that. Perfectly clear. I've switched the HW off at the programmer and will run the tests once the family have showered this evening and partially depleted the hot water. Stand by.

 

[MeldrewsMate]

Your statement from today at 5:46

Yes, the pump runs when only CH is on, as does the boiler; the CH powerhead moves too and the rads get hot.

seems to contlict with that of your original post

If I then demand CH with HW already demanded the boiler still doesn't fire. If I now switch off both HW and CH before then demanding CH only, the boiler fires. If I now demand HW with the CH already running, I get HW.

There may be a couple of possibilities...
1. You've mis-wired, but it looks substantially correct. The important point is that the yellow wire in your terminal 13 should contain both orange wires, plus the lives to the pump and the boiler demand (often referred to as switched live, SL). If that is correct, and both valve grey wires are in a permanent live terminal (your T11), there will always be a boiler demand when either or both valves are open. It seems, though, that does not fit with your symptoms.
2. You may have a failing programmer. I have seen a fault on others where the programmer's internal power supply is failing, and will not continuously power 2 output relays. This doesn't fit your symptoms either.

My guess is that, assuming the wiring can be proved to be correct, you have an intermittant fault on the boiler, and it's nothing to do with the valve.

 

[Charles Victor]

No contradiction, MeldrewsMate. Statement One is when CH is the first circuit switched on. Statement Two is when CH is switched on with HW already on.

Thanks to your item 2 and the crystal clear test instructions from Echo the husky I do wonder though if we are on to something. Testing worked out precisely as it should have done in terms of when to expect a voltage and when not, but the voltages are all lower than expected at 231 or 232 volt versus the expected 236 volt if I test a mains socket. The other thing that is odd is that during the testing - which I repeated multiple times to be absolutely sure - when demanding HW only I had three separate symptoms: Most times the boiler didn't kick in but once it did and once more it didn't initially but did after a several minute delay. In all cases the powerhead lever moved to full deflection and the pump started (and continued) running as soon as HW demand was placed on the circuit.

Perhaps therefore the original HW powerhead hadn't failed as I assumed (cold water and the HW powerhead lever wasn't moving when it should) and the fault is actually the boiler or controller?

The controller is the common as muck Lifestyle LP522.

 

[Echo the husky]

Ignore the exact voltage as long as its somewhere around 220-250 ish volts you are fine.
Sounds like a loose connection to the boiler connection. If the valves are moving when they should their motors are ok and so is the programmer. the fault will be around the switched output, the pump comes on all the time so that rules out the valves micro switches. That just leaves the connection to the boiler, which should be connected together with the pump live.

 

[Charles Victor]

Thanks for that. I presume you mean circuit 13 in my photo? If so I will do as I intended anyway and split it in to two pairs of wires using 13 and 14 with a bridging wire on the opposite side of the two chocolate blocks.