Drayton MiTime T721R

[westo]

Hi,

I've just fitted the above 2 channel programmer which was a straight swap i.e. L, N, HW off, CH off, HW on, CH on.

It works fine on the timer, both HW and CH come on, and the HW will work on the boost button. However, the CH won't work on the boost button.

Any ideas appreciated?

 

[mogget]

I have the multi channel version. Providing you are selecting the zone using the up/down buttons before attempting to use the +hr / adv buttons, I would say it must have a software fault.

Did you get a manual with it?

 

[westo]

Cheers for reply. Yeah I've selected the correct setting, the light on the mitime comes on but the boiler doesn't fire.

By way of a check, today I've managed to get the CH boost/advance working...but only if the hot water is switched on at the same time.

Shortly after fitting this, I also had to change the 3 port valve in the airing cupboard which was again a straight swap.

In the joint box I noticed 2 wires that weren't connected to anything (and looked like they never had been ie no insulation trimmed back).

Does any of this shed any more likely causes?!

 

[mogget]

Have a look at this http://www.electriciansblog.co.uk/wp-content/uploads/2012/02/Y-Plan-Biflow-Wiring-Diagram.png and follow it all through. bear in mind that your terminals may not be numbered in the same way, the wiring in the junction box may be in a different order, and your pump may be connected directly to the boiler if it is a modern one.

Did you change the programmer due to a fault?

Either way, the display on the programmer should show whether the +hr or adv buttons have been pressed. Maybe there's some setting in the installer menu that needs to be changed - I don't remember all of it like the back of my hand!

I would be looking for a break in the hw off wire somewhere. But I'm just a diyer!

 

[westo]

Thanks for that.

Just a question, why would a break in the HW circuit affect the CH? And if there was a break in the circuit, wouldn't the HW not work (or nothing would work on the timer at all?)?

I appreciate your help, I'm just getting my head round how it works!

 

[mogget]

I must admit that I don't know every possible fault on a y-plan, but the HW off is necessary for the heating to work properly.

If you changed your programmer to upgrade it I would put the old one back on and see if it all works. Depending on where you bought the mitime from you may be able to get it swapped.

Was the system functioning correctly before you changed the programmer, or do you have a fault that was present before and after? If it was working before you changed the programmer and the pinout on the programmer is the same, it would suggest a faulty programmer. I suspect as you can't get the programmer to show +hr on heating, it is probably faulty.

 

[westo]

The programmer shows (on the display) the +1hr added onto the time period and the light on the programmer comes on, it's as if there is a break somewhere else.

I think I need to investigate what these spare wires are in the joint box.

However, logic would say that if the heating works when the water is on, it should work when it doesn't?! I don't know!!

 

[mogget]

Follow each wire in turn, HW ON, HW OFF, and CH ON. You will need a multimeter and the knowledge of how to use it safely. This does involve working on live electrics, so if you're not sure, I would advise you call a professional.

 

[Whitespirit66]

As said above to rule the programmer as faulty or not, check the outputs from Mitime.

For the ch only/boost, you should have both 'ch on' and 'hw off' terminals live at the programmer. If you don't have both live, then the programmer is at fault.

This diagram will help -

http://octaveblue.co.uk/c_heating/ch_only.htm

 

[westo]

Thanks for the replies.

I've been reading up on how the mid position valve works and working out what the loose wires are in the joint box. It seems that one of the loose wires is a blue wire from the cylinder stat, and there is only 1 other wire in the grey wire terminal (2 in total - there should be 3; one grey wire from valve, one from programmer and one from the cylinder stat).

This leads me to think that the cylinder stat cannot power 'off' so no power is getting to the boiler unless water is also called for.

I'll investigate tomorrow...