Wiring new programmer back plate

19 Nov 2021
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United Kingdom
Currently have a horstmann h27xl programmer for our heating/water but it’s seems to have failed today as it won’t fire the boiler when pressed for hot water…. Was looking at a replacement programmer the Drayton 522 or 722, but I’ve noticed the back plate are different, the horstman is numbered 1-6 (but 3 and 6 empty)but the Drayton is only 1-4 …. Could someone advise me if I was to buy the Drayton one tomorrow what wires that are in 1,2,4 and 5 on the Horstmann go we’re on the Drayton?

many thanks
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What is it that leads you to believe it is the programmer that doesn't turn on the boiler for hot water ?
If I turn on the hot water on the programmer and the boiler doesn’t turn on what else could be at fault?

I press the button on the programmer for central heating and the boiler fires, I press so hot water and it doesn’t, so I was thinking something within the programmer has failed and not making the connection to switch on the boiler

if you have any other ideas of why all a sudden it wouldn’t work please let me know what I can try because at the moment I’m using the immersion heater to heat the water in the cylinder.

Thank you
When switching programmer to hot water ,does the red light come on ?
Cylinder thermostat ,zone valve,wiring issues could also cause the boiler to fail to ignite.
Do you have a Y plan or S plan set up ?
( What motorised valve or valves do you have )?
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Yes the red light comes on but I thought it might not mean much as maybe it’s coming on as when I press the button it would come on because it’s getting power but not sending the power.

I believe it’s S plan. I have 3 motorised values, 2 down stairs, 1 which runs the downstairs radiators and and the other which controls the upstairs radiators, then the 3rd value is beside the hot water cylinder which I assume is the only one that controls the hot water. (If I was to push the lever to Manual, would the boiler then fire if this was faulty)

No ,that will only open the mechanical port to allow water thru the valve body and onward thru the hot water cylinders coil . However ,if you run central heating as well ,and manually latch the hot water zone valve open ,you will heat the cylinders water too. Unfortunately this will take the hot water cylinders thermostat out of the loop ,so the temperature of your hot water would get a lot hotter than you are used to as the cylinder stat isn't controlling it .
Could be either ,or the cylinder stat . Testing voltages present at the wiring centre would establish which it is.
I would say the motorised valves motor failure is probably more common than the programmer .
Randomly exchanging parts is generally the least cost effective method of repair. You need someone who knows how to use a multimeter and understands how the system is supposed to work

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