S plan probable wiring fault?

[Best]

I replaced a programmer on an S plan system in a small bungalow and when checking zone valves operation, I discovered an existing problem.
There is the usual 2 port MV for radiators, (controlled with hall stat), plus a second 2 port MV for hot cylinder, (controlled with cylinder stat).

Programmer on hot water only setting, it works fine and cyl stat turns it on and off.
Problem is on radiators only setting, the rads work but power is also then to the cylinder MV. Cylinder stat then becomes nonfunctional.

Customer had said her hot water was always very hot.
Wiring fault I guess in wiring box?
Work is all very amateurish looking.
I can’t easily open the wiring box due to some idiot piping across the cover.

 

[Riley]

Sometimes better all round just to start again

 

[Millsy 82]

Not on gravity on programmer? Whip the programmer off and put a link inbetween the live and heating and see if you still get power to hot water side, if not I would be looking faulty programmer.

 

[Last Plumber]

Have you tried disconnecting the brown to both MV's and testing switched live to each in turn from the Programmer?

 

[Best]

Am going to have to rethink this.
I completely forgot that there would be a gravity setting in the programmer!
So will check that first.

The cylinder would have been very hot previously in retrospect due to the cylinder stat not strapped to cylinder.
Although I suspect it also was constantly heating when rads were on with old programmer

 

[Burger]

Am going to have to rethink this.
I completely forgot that there would be a gravity setting in the programmer!
So will check that first.

The cylinder would have been very hot previously in retrospect due to the cylinder stat not strapped to cylinder.
Although I suspect it also was constantly heating when rads were on with old programmer

Ah the joys of something clicking into place, I love that feeling, although not after making the air blue and tearing my hair (or lack of ) out

 

[Chuck]

I completely forgot that there would be a gravity setting in the programmer!

A common 'gotcha', you're in good company.

If that is the problem and you convert to independent CH and DHW, don't forget to check whether the modified system needs an ABV fitted/adjusted because the cylinder loop will no longer be providing a bypass.

 

[Best]

Ah the joys of something clicking into place, I love that feeling, although not after making the air blue and tearing my hair (or lack of ) out

That is what is great about a second opinion from here, - it means I approach it again differently.
You know what it is like on a job, - I had half an hour to check it all and decided not to get too involved in the wiring.
Job didn’t give me much confidence when you see the standard of work, - cyl stat not strapped to cylinder and just lying on floor and a copper pipe fitted in front of the wiring box cover.

 

[Best]

A common 'gotcha', you're in good company.

If that is the problem and you convert to independent CH and DHW, don't forget to check whether the modified system needs an ABV fitted/adjusted because the cylinder loop will no longer be providing a bypass.

That’s a good point!
I think there is no bypass valve anywhere. Doubt if the installers knew what it is.

 

[Coby kenny AGUILAR]

I replaced a programmer on an S plan system in a small bungalow and when checking zone valves operation, I discovered an existing problem.
There is the usual 2 port MV for radiators, (controlled with hall stat), plus a second 2 port MV for hot cylinder, (controlled with cylinder stat).

Programmer on hot water only setting, it works fine and cyl stat turns it on and off.
Problem is on radiators only setting, the rads work but power is also then to the cylinder MV. Cylinder stat then becomes nonfunctional.

Customer had said her hot water was always very hot.
Wiring fault I guess in wiring box?
Work is all very amateurish looking.
I can’t easily open the wiring box due to some idiot piping across the cover.

Two ports have a permanent live at all times which is usually a grey wire

That cyl start won't work because is isn't receiving power from the programmer

Time (programmer) - temperature (stat) - control (MV)

Everything has a sequence

 

[Best]

Two ports have a permanent live at all times which is usually a grey wire

That cyl start won't work because is isn't receiving power from the programmer

Time (programmer) - temperature (stat) - control (MV)

Everything has a sequence

Yes, I knew that. Had no time to check the wiring, but will do.
Danfoss MVs, which can be very unreliable, but both are working ok.

 

[Last Plumber]

I completely forgot that there would be a gravity setting in the programmer!

Probably because they're pimple sized dip switches that are almost invisible to the Human eye. Let's face it, most systems have been fully pumped for a good while now and remembering to check that is not always in the front of our minds.

Remember the Landis & Gyr Clock? the one where you slid the selector to the far end and twist locked the CH and DHW together.
No mistake there! Plus it was probably 50/50 which way it wanted to be, if not more toward 10 programs?

 

[Ready Steady Gas]

Just a thought,

Check the orange cable from the CH MV has not been mistakenly linked to the grey HW MV cable in any way. If that makes sense?

That would also be a possible cause of the fault you are describing.