Honeywell ST1000

[RancidPants]

Hi all First post - although I have been reading for a while.

I moved into my new house 3 months ago. I have a Honeywell ST1000 programmer which is just like this one (the brand name is different):

haven't used the central heating/hot water timer until now. I have just moved the switches onto 'Constant' as and when required. This works fine.

Recently I wanted to time the heating / water to come on in the morning but I've noticed that the clock mechanism doesn't work. Does this mean it's knackered? The switches work okay, and as I rotate the dial by hand, the heating / water comes on and off as the dial passes the pegs. I would have thought that if the unit is connected correctly, then the clock would be working at all times.

If the controller is bust, I could obviously get the one I've mentioned above from Screwfix. But I think it would be a good idea to put a modern digital one in. I don't want one with a built in thermostat because the controller is in the airing cupboard. Am I right in thinking they are pretty much universal? My heating system is (I think) fully pumped, having just two water pipes coming from the boiler, one pump in the airing cupboard, two automatic valves of some sort, one three way and one two way, all connected up to a Heatrae Sadia Megaflow (mains pressure hot water tank).

Sorry to sound like such a novice (I am by the way). Thanks for any help.

Luke

[Christian McArdle]

They are relatively simple to replace. However, I don't know if the one you have uses some sort of standard backplate, or if you are going to need to wire up the new programmer. Some programmers have "volt free" switch outputs. Others have outputs hard wired to 230V. You can fit a volt free programmer to a 230V system, but you might not be able to fit a 230V output programmer to a system requiring volt free contacts. However, most systems are quite happy with the 230V signalling.

It is important to not touch the 2 port valve wiring. The 3 way valve is used to control your system as in many central heating systems. The two port valve is probably a very important safety device that should the Megaflo requires to remain safe. Do not modify the controls to this one. It is an emergency cutout.

Christian.

[geoff]

In message , RancidPants writes

OK - the easiest thing to try is replacing the 0.1 uF capacitor on the back of the timer. If that works, you're back in business, if not, the motor's prolly gone and your best bet is to buy a new one

To remove the timer, undo the two screws on the underneath of the timer, thumbs underneath the timer and lift up - they are quite tight

[RancidPants]

Thank you for your help. Based on what you said I have taken the front off the controller and found out a bit more about the wiring.

It has a nine terminal backplate. Live, Neutral and Earth make up 3 of them. No problems there.

The other 6 are split into two groups of 3, labelled "ON", "C" and "OFF". I have worked out that the first group of 3 terminals is for the CH and the second for the HW.

The Live wire is daisy chained to the two "C" terminals. I think I am right in saying therefore that it a 230V signalled system.

After using my multimeter I have worked out that a circuit is completed between the respective "C" and "ON" terminals whenever the HW or CH is demanded by the controller. So, it's all making sense. The two "ON" terminals each get 230V when demanded to by the controller, for either the HW or the CH.

I haven't yet worked out the "OFF" terminal. The "OFF" terminal for the CH is not connected to anything. It looks like the "OFF" terminal for the HW is connected to the tank thermostat is some way. My assumption at the moment is that if the "OFF" terminal gets 230V then it overrides the connection between "C" and "ON" and breaks the circuit. Probably when the water gets up to temperature.

However, if this is the case, I would have thought the "OFF" terminal for the CH would be connected to the wall thermostat in some way.

Anyway, to cut a long and fairly boring story short, I am fairly confident that I can wire up a new digital controller once I know about this "OFF" terminal and can have some reassurance that what I've written above it correct. So, if any of you can give me the green light, I'm going to go for it!

You may be right here Christian. The two port valve is situated between the three port valve and the Megaflow heating coil entrance. I thought it might be something to do with biasing the boiler output towards the radiators until they heat up, before sending output through the HW heating coil.

Thanks again

Luke

[Christian McArdle]

The 'C' stands for common. When heating or hot water is demanded by the controller, the 'C' is connected to 'ON'. When it isn't, the 'C' is connected to 'OFF'. Some methods of wiring three port valves call for some complicated linkages between the programmer and the tank thermostat. This is quite normal.

Almost any programmer would work for your system. The differences between them are basically whether the 'C' terminal is internally connected to live or not. As this needs to be done anyway on your system (which is the normal case), this isn't an issue.

Christian.

[RancidPants]

Thanks for the advice.

I've ordered a Invensis Drayton Tempus 7 programmer from InspiredHeating.co.uk. I would have got one from Screwfix (they're cheaper) but I thought they were all a bit pug-ugly. As I have now decided to relocate the programmer to the kitchen, I spent quite a lot of time choosing one I liked the look of!

No doubt I'll be back in touch if I manage to make a complete balls-up of the job.

Luke