I have a Y plan central heating and hot water system with a 3 port mid posi tion valve. I decided I would label up all of the wires in the wiring cent re for my own benefit. When I came to the HW ON wire from the timer (Drayt on Tempus Seven) it looks like it is permanently live and that the switchin g off of the HW is actually controlled by the HW OFF from the timer or the tank stat satisfied feed.
This all appears to works OK, I was just expecting the timer to only reques t hot water during the defined time period rather than it being controlled by HW OFF feed outside of the time period i.e. only HW ON or HW OFF being l ive at any one time.
The Tempus seven should have a permanent live and neutral feed from the wir ing centre from it there are two switched lives one to the cylinder stat (H W) and one to the room stat. These are only live when either is on a timed period or you have set HW or heating manually.
So it may be a faulty timer that has the switched HW ON permanently live or its wired incorrectly on the timers back plate.
I did have a go at getting the timer off its back plate but its been tiled around. Looks like I need to persevere.
I also tried to find a manual from the Tempus Seven but could only see the newer white ones. Mine is (I guess) a much older brown one. It was probably put in place when the house was built in 1989.
How are you defining "live"? Is this by measuring 240v relative to neutral, or by putting your thumb on the end of a mains detection screwdriver and seeing a glow - 'cos these two options may give different results.
What else was on when you were doing this? If there was a CH demand to the boiler, and if the HW stat wasn't satisfied, mains would be back-fed to the timer's CH-on terminal even when set to OFF on the timer. Could this be what you were seeing? What happens if you disconnect the wire from the timer's CH-on terminal? Is the terminal itself still live? I'll wager it isn't!
position valve. I decided I would label up all of the wires in the wiring centre for my own benefit. When I came to the HW ON wire from the timer (D rayton Tempus Seven) it looks like it is permanently live and that the swit ching off of the HW is actually controlled by the HW OFF from the timer or the tank stat satisfied feed.
quest hot water during the defined time period rather than it being control led by HW OFF feed outside of the time period i.e. only HW ON or HW OFF bei ng live at any one time.
Live as in 240v registering using a multimeter across the CH ON wire and ne utral.
At the time, the timer was set to NO heating and NO hot water. The CH ON w ire had power to it which was being fed through the tank stat common termin al. As the hot water was up to temperature the return was being fed throug h the satisfied terminal.
My next step was (as you have recommended) to check what is actually coming from the timer by isolating it from the wiring centre and to also check th e wiring on the back plate of the timer.
I might have to leave the second part until the weather warms up as I could nt get the timer off the face plate because its tiled around (I think it un screws from the bottom and swings up on "hinges" at the top). It felt like the "hinges" were going to snap when I tried it. If that happens then I w ould probably have to replace it. The family wouldnt be very happy with a heating outage :-(
OK, I have just disconnected the timer HW ON wire and tested on and off and it is working OK. So it looks like (as I think you guys suspected), it is feedback.
If the timer is set to HW OFF and the cylinder stat is satisfied then the 240v would be fed back down to the timer HW ON. Does that sound right?
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