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My friend just rented an appartment (in the UK), and during the inventory the janitor showed her the programmable water heater, and said it was configured to turn on for a few hours during the day.

However, due to (1) extremely high energy bills, and (2) apparent contradiction w.r.t. the instructions, we suspect the janitor may have inversed the program, leaving the water heater on for almost the entire day. I cannot convince myself either way, so I'd like some advice about it.

Here's what the panel currently looks like:

Current status of the water heater programmable dial

And here's the instructions, printed and glued to the back of the panel door (the relevant part is the lower half):

Instructions for the water heater

These instructions seem to contradict what the janitor said: the example says "the jumpers are pushed in from 9 a.m. to 10 p.m." in the picture, which would indicate that the actual heater is on during most of the day (and night), the opposite of what the janitor said. However, since he seems to be working for the residence for several years, such a mistake is very unlikely. But then why do the instructions seem to indicate the opposite?

Note: there is no easy way to physically confirm if the heater is on or off at a given moment: there are no LEDs on the panel nor on the heater itself, and there is no discernible noise during the transition. The energy meter is outside and due to other appliances (e.g. refrigerator, towel rail, ventilation, etc.) you can't easily isolate the energy consumption.

  • Does the heater have a thermostat, or is it always heating when the timer is on? – Tester101 May 6 '15 at 1:34
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    The little blue knob thing in the upper left of the dial is labeled as the "contact status display switch", which I would assume means that it displays the status of the contact. In the current photo it appears to be in the OFF position. Does this knob turn or move when the tabs are in the opposite position? – Tester101 May 6 '15 at 1:54
  • It also appears that "ON" and "OFF" are relative, depending on how the device is wired. According to the label, in one position the contact is closed between terminal 1 and 2, and in the other position the contact is closed between terminals 2 and 3. So you can say that terminal 2 is "common", and will have the incoming feed connected to it. The line feeding the heater will either be connected to terminal 1 or 3. Do you have any idea which terminal the wire feeding the heater is connected to? – Tester101 May 6 '15 at 2:03
  • The heater has a thermostat. I have no idea which terminal the wire is connected to. I will tell my friend to check the contact status display switch, thanks for noticing that, and will report about it. – anol May 6 '15 at 7:43
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I agree it's a little unclear what the right way is.

Why don't you try a test. One evening push all the pins one way, run the hot water for a bit to flush some water, then leave it overnight. In the morning if you still have hot water then the heater was on overnight. If you aren't confidant, repeat the same the next night with the pins the other way.

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I'll agree that it's difficult to tell from the image what in and out are.

If you had an ammeter, you could test for current flow to determine if the heater was on or off. You'd wait until the timer says the heater was off, go to the heater and clamp the ammeter on the ungrounded (hot) conductor. If the meter shows a reading, it means the heater is on. You'd then do the same when the timer says the heater is on.

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    I'm not sure I agree. According to the diagram it looks like "IN" means towards the center, not back. – Hank May 6 '15 at 0:43
  • @HenryJackson I think you're right. In the photo, it's hard to tell which tabs are pushed in (especially on a small phone screen). – Tester101 May 6 '15 at 1:11

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