For those who don't know, this is the type of thermostat where you set the time by which you want the house to reach the required temperature and the stat works out when the boiler should come on, depending on the overnight drop in temperature. There has always been a nagging doubt as to whether they do what is said on the tin.
I have now worked out a way of checking, so here it is:
View media item 25509
How does it work?
The clock is an old 240V alarm clock which resets to 1200 if the power is turned off and on. (Normally it has a 9V battery to keep the clock going during power cuts, but this has been removed.) The 240V AC is a permanent supply. The red lines are links I have put between the relay contacts. The whole device (apart from the clock) fits into a standard surface mounted switch box with a blanking plate cover drilled to take the reset switch.
When the thermostat first calls for heat, the relay is energised via the normally closed contact of switch A, which starts the clock. The relay switches over, so the clock and the relay are both powered from the 240V AC supply via switch B. The thermostat is disconnected, so it can do what it likes. This also prevents voltage from the 240V supply getting onto anything else connected to the thermostat, e.g. a motorized valve.
When you get up in the morning, say at 7am, and the clock shows the time is 0200, this means it went on two hours earlier, i.e at 5 am. To reset the system you just press the switch, which breaks the circuit to the relay.
If you use the timer every day for a reasonable time you will soon find out if the times change according to the weather. It might however be advisable to have a Max-Min thermometer hanging next to the wall stat so you can relate the start time to the minimum overnight temperature.
I will report my findings when the heating goes on.
I have now worked out a way of checking, so here it is:
View media item 25509
How does it work?
The clock is an old 240V alarm clock which resets to 1200 if the power is turned off and on. (Normally it has a 9V battery to keep the clock going during power cuts, but this has been removed.) The 240V AC is a permanent supply. The red lines are links I have put between the relay contacts. The whole device (apart from the clock) fits into a standard surface mounted switch box with a blanking plate cover drilled to take the reset switch.
When the thermostat first calls for heat, the relay is energised via the normally closed contact of switch A, which starts the clock. The relay switches over, so the clock and the relay are both powered from the 240V AC supply via switch B. The thermostat is disconnected, so it can do what it likes. This also prevents voltage from the 240V supply getting onto anything else connected to the thermostat, e.g. a motorized valve.
When you get up in the morning, say at 7am, and the clock shows the time is 0200, this means it went on two hours earlier, i.e at 5 am. To reset the system you just press the switch, which breaks the circuit to the relay.
If you use the timer every day for a reasonable time you will soon find out if the times change according to the weather. It might however be advisable to have a Max-Min thermometer hanging next to the wall stat so you can relate the start time to the minimum overnight temperature.
I will report my findings when the heating goes on.
