Using a thermostat and a programmer help please

8 Jun 2011
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United Kingdom
The answer is probably very simple but I can't work it out can anyone help please.

We have.
Randall 4033 programmer near the hot water tank.
It has a timer with red and blue adjustable pointers A,B,C,D
A and C starting when we want the programmer to turn stuff ON and B and D when we want stuff OFF
For both the heating and hot water it has a separate On and OFF switch.

We also have a Drayton thermostat in the front room.
Adjustable from "Frost" to 30 degrees C
There is a red dot between 15 and 25.

I have three questions please.
On the Drayton what is the significance of the red dot, e.g. does it just indicate this is an optimum setting?

Does the Drayton control the Randall when it is running both on a "Timed" setting and when it is switched manually to ON?

What effect do we have on the Randall when we switch from "Timed" to manually turning either the hot water or the heating ON and then OFF?

I have found we need to turn the timer at least twice to reset the automatic switches on the dial but I am not sure if manually turning the systems ON and OFF while the timer is running means we have to do the same reset when we revert back to the "Timed" option.

I hope this makes sense.

Thanks for looking,
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Sorry I can't tell you what the red dot on the room thermostat is for.

The Drayton thermostat will only work to switch the heating On/Off when the 4033 programmer allows it to, this can be either in timed or manual mode and it works the same way in both.

So the 4033 programmer would either be set for heating Manually-On using the switch, or Timed-On using the dial tappets. The room thermostat would then be able to control the room temperature by switching the boiler on and off.

If the programmer shows heating Off (manual or timed) the thermostat can do nothing.

Switching from manual On (or Off) to Timed should get you back into the correct timer sequence shown on the dial without having to reset anything
The red dot means it is "on" and calling for heat.
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Thank you for these helpful replies.

Just to clarify. the red dot is just that, it doesn't illuminate in any way.

We now know we can swap both the heating and water between manual and timed operation without having to keep resetting the programmer.

Many thanks and a Happy New Year,
Last night the programmer automatically timed out as set.
We manually switched it to ON.
Later we switched it to OFF (not timed)
2am it came on automatically and wouldn't turn off until I rotated the dial.
3am it came on automatically and wouldn't turn off until I rotated the dial again.

Switching manually to OFF had no effect on either occasion (I did wait for it to stop both times).

This morning.
Switched it to "Timer". It came ON and went OFF automatically as expected.
I then turned the programmer unit off using the switched power supply.
Rotated the dial three times to try and clear any previous settings.
Turned it back on and kept the "Timer" position (now at an OFF period between tappet B and C).
It stayed off.
Switched it manually to ON and it came on.

I will see what happens tonight.
If the same problem reoccurs I assume we will need a new programmer?

Looking at the simple internal wiring diagram for this programmer it shouldn't be possible to get the Heating_ON voltage when the manual switch is set to OFF but that may not really represent what happens inside the unit.

Ideally when this fault occurs you would want to check for this (240V) voltage with a multimeter in the wiring centre just in case the boiler is somehow firing up for a different reason.

Do you have any motorised valves in the system?

One of these

Or two of these


Thank you VERY MUCH for taking the trouble to provide all this information and advice.

I might have come across the answer???
We bought this house and moved in last week so are still finding our way around the property and appliances/systems.

For some reason the gas boiler for the heating is in an outhouse attached to the rear of our house.
I went in just now to look and found a unit marked "Grundfos Frostat" attached to one of the pipes on the boiler with wires that disappear into the house.
These wires look very similar to a pair going into the 4033 programmer in addition to the one going from the main power switch.

Could this Frostat unit be switching our central heating on by overriding the 4033 programmer settings?
If so I assume that by turning the thermostat in our front room down to frost setting we will keep the pipes/boiler in the outhouse free of ice while also keeping the heating in the house down to a minimum while we are asleep.

I would very much appreciate your thoughts,
Yes the pipe frost stat would usually be wired so it overrides everything and can always switch on the boiler if the pipe temperature gets down anywhere close to freezing.

(Don't confuse this with the room thermostat as the pipe frost stat operates totally seperately from the room thermostat and it's frost setting.)

It would depend how it was wired as to which parts of the system received heat from the boiler when it fired up, generally it's the central heating.

This is reassuring news.
It explains why an electrical unit apparently without any power supply or battery appeared to activate itself in our airing cupboard. :)

We can now sleep easy without worrying about either the boiler/pipes freezing up or the heating system failing during a cold bank holiday.

Being ex bomb disposal it also reassures me on other levels. :)

Once again thank you for all your help with this,

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