Rewiring

[Fayrana]

My central heating timer (Potterton Mini Minder) has finally given up the ghost. I have purchased a basic replacement not to dissimilar to the mini minder which is a Horstmann 425 Tiara. I was hoping the wiring would be exactly the same but it is not. the miniminder had 3 wires in addition to the L and N which are Blue , yellow and red which go to numbers 2,3 and 4 on the backplate leaving no.1 empty. The new backplate has 6 slots in addition to the L and N which state from L to R, Off, C, On, Off,C, on, L , N
What I need to know is where the blue,yellow and red wires go on the new set up?
Any idea's folks.
thanks in advance.

 

[D_Hailsham]

My central heating timer (Potterton Mini Minder) has finally given up the ghost.

What is wrong with it?

The Miniminder had 3 wires, in addition to the L and N, which are Blue, yellow and red which go to numbers 2,3 and 4 on the backplate leaving no.1 empty.

I would expect no 1, sometimes, to have a wire in it; but never no 2.

 

[Fayrana]

Just double checked. wires in 2,3, and 4 not No.1

 

[D_Hailsham]

Just double checked. wires in 2,3, and 4 not No.1

Then there's something strange/wrong.

You didn't answer my first question - what is wrong with the Miniminder?

Has anyone fiddled with it recently - e.g a friend or a plumber/"heating engineer"?

Can you have heating on without hot water on?

I need to know where the blue wire in terminal 2 goes to (it shouldn't be there!). Can you find out?

 

[Fayrana]

sorry, the miniminder's clock/dial no longer rotates.
nobody has touched the system. Believe this is how it was installed prior to us moving in. I've been here 8 years.
No I can't have heating without water. I can have water without heating though.
It would appear at face value all three wires go through the wall within the insulation in to the garage and then feeds in to a double sized socket box. Wires come out of the socket box to the boiler and pump?

 

[D_Hailsham]

sorry, the miniminder's clock/dial no longer rotates.
nobody has touched the system. Believe this is how it was installed prior to us moving in. I've been here 8 years.
No I can't have heating without water. I can have water without heating though.

Thanks for the info.

The fact that you cannot have heating without hot water means that you have a pumped heating, gravity hot water system. You will have either three or four water pipes connected to the boiler.

But this doesn't explain why you have a wire connected to terminal 2.

all three wires go through the wall within the insulation in to the garage and then feeds in to a double sized socket box. Wires come out of the socket box to the boiler and pump?

Can you take the cover off the socket box, take a pic and post it?

If not, a detailed list of what is connected to each terminal will have to do.

Details of your boiler (make and exact model) are also helpful.

 

[Fayrana]

The boiler is badged as a British Gas 330+. If was fitted by BG about 18 months ago but they did not touch any of the wiring. I have uploaded a picture of the back plate, the box an a longer shot of each. There are 3 pipes in to the boiler, 2 the top and 1 at the bottom + overflow at the bottom. Thanks for your continued help. I have created album and hopefully uploaded for you to see.

 

[MANDATE]

I also have mini minder which had same problem. Could use it manually but clock had stopped working.
It is working again now. problem was either dry motor and I applied a touch of WD 40 or it may have not have been making contact on the neutral contact.
I have gravity HW and pumped CH.
terminal 4 is for CH ON. The wire from here goes to to the pump via the room stat.
terminal 3 is for HW ON The wire from here goes to boiler via cylinder stat and/or boiler stat
terminals 2 and 1 not used.

 

[D_Hailsham]

The boiler is badged as a British Gas 330+. If was fitted by BG about 18 months ago but they did not touch any of the wiring.

Looking at the pic of the boiler, I can see only two water pipes (at the top). I can also see a mid-position valve on the right. So your system is not gravity HW/pumped CH, it is a fully pumped one. This means you should be able to have any combination of HW and CH. The reason why you are restricted to HW only or HW + CH is that the boiler installer didn't bother to alter the wiring - probably didn't know what to do!

It really needs the wiring corrected, which is possible via the internet, but details will be required about where each wire of every cable connected to the junction box (JB)goes, listed by JB terminal no.

The Horstmann control is suitable, but it is a bit restricted as the same times are used for heating and hot water.

 

[MANDATE]

this should give you the information

http://www.horstmann.co.uk/downloads/ElectronicDocuments/Central-Heating/425-InstallationGuide.pdf.
As far has I can make out to control mains supply you have to link L to 2 to 5.
terminals 3 and 4 on mini minder are replaced with 1 and 4 on tiara.

The blue in terminal 2 of mini minder remains a mystery.

 

[Fayrana]

Mandate, Thanks for the comment. The problem I appear to have is that I have a blue wire going to terminal 2 as shown in photo in my album. As I have 3 wires in addition to the L and N, where do they go on the new timer I've purchased?

 

[MANDATE]

Now it turns out to be fully pumped, I'm thinking the mystery 'blue' was intended to be the HW OFF wire but why was it in terminal 2

 

[Fayrana]

Guys,
thanks for all your comments and advice. The current system still works although I have to turn the clock manually. Might try and give it a squirt of WD, have nothing to loose.
I am under contract to BG and annual check is booked for a weeks time. Might see if timer is covered in contract otherwise will have to get a sparky.
thanks again.

 

[Hugh Jaleak]

Might have a case for recompense from BG. They've fitted a new boiler, yet the system cannot have been tested correctly on completion otherwise the fault with the wiring would (should!) have been picked up!

System should (if/when wired correctly) allow seperate control of heating and hot water. It does beg the question what (if any) thermostatic control is available on the system, and if none (or none on HW) I would think the installation doesnt comply with current building regulations!

For information, the two pipes connected to the top of the boiler are flow and return to the system. Flow is split via the 3 way valve to the radiators and hot water cylinder. Valve should open to either (independantly) or both depending on demand from appropriate thermostats. Bottom of boiler, copper pipe is gas supply, plastic is condensate drain.

 

[Fayrana]

Ok. I'll see what they have to say when they service the boiler.
Thanks