Strange problem with Heating Programmer - Please help

[Handaloo]

Please help!

I recently changed our thermostat in the hallway and wired it incorrectly. This caused our heating programmer to short and burn out. SO, I got a friend over who's an electrcian (who is the first to admit he's not great with heating electrics) who then wired it in correctly (or so we thought).

Today I got a new programmer, plugged it in with the thermostat at zero, and it worked. I then slowly increased the thermostat temp bit by bit and at around 15 degrees, when it clicks, it once again shorted the fuse (luckily only the fuse this time). I then contacted my friend who avised on another option for the wiring which I did. It now works, however the central heating just stays on. As soon as the plug next to the programmer comes on (the type with a switch and a fuse, apologies for the lack of correct names for things) the central heating comes on, and I cannot turn it off.

Here is a link to the wiring for the thermostat: (I have the RMT230)

http://danfoss-randall.co.uk/PCMPDF/RMT230.pdf

I have have it wired in as follows:

4 - Blue wire
1 - Red Wire
3 - Yellow Wire

Anybody know what is wrong? I understand it will be hard to tell from the info provided, so if there is anything else I can supply, I will certainly try!

Thanks

Handaloo

P.S the programmer I have is the Danfoss Randall FP715si

 

[MANDATE]

Hi! I've just had a look at the wiring diagram and my understanding of it suggests the 'live' wire goes in at terminal 1 and the 'switched live' comes out at terminal 2. when 2 is live power is also supplied to the accellerator and then the neutral comes out at terminal 4.
No doubt blue will the neutral but you need to establish which of the other two is the 'live'?

 

[MANDATE]

Furthermore just verified a friend stat has the yellow as live and red as switched live. I reckon yours is the same.
If you put the live in at terminal 3 switched live comes out at 1 and heating will never be off because the accelerator will not be in the circuit.
so I think you need yellow in 1 and red in 2.

 

[kevnurse]

That circuit diagram forms a very small part of the boiler controls and it assumes that the rest of the circuit is properly wired, including the thermostat and the zone valve motors, etc. Best advice is to bite the bullet and get a heating engineer out.

 

[Space cat]

I think you have two problems here. Firstly, if you really can't turn the heating off with the programmer then I'm afraid that it is damaged. You just can't see it. It may appear to work but an internal switch is short circuit.

Secondly, if the thermostat doesn't appear to work try turning it right UP. I think you'll find that your heating will then go off - and stay off until the house cools to a sufficiently high temperature!

Look carefully at the diagram in that link you posted. Mandate is correct. Four is neutral, and also the cause of your blown programmers. One is live in from the programmer and two, not three, is switched live out. You can work this out from the way the accelerator heater is connected. Three becomes live only when the temperature exceeds the set level; it's for cooling, or else for motorized valves that must be driven shut.

The colours of the wires in terminals one, TWO and four are meaningless unless you know which one goes where at the other end. You seem to have established, at the expense of two programmers, that blue is neutral so leave that in terminal four. One of the others will be live whenever the programmer is requesting heating - which yours always is! That one goes in terminal one. The third wire goes in two and you leave three empty. All you need now is yet another programmer.

PS: That thing with a switch and a fuse is called a switched fused connection unit (switched FCU for short).

 

[Handaloo]

Ok, we seem to be getting somewhere.

MANDATE, seeing as I can change the wires with the thermostat set to zero and it doesn't blow up, I tried your previous suggestion of yellow in 1 and red in 2, and it now doesn't come on constantly!

It now doesn't come on at all, until I turn the thermostat up until it clicks. However the programmer seems to have no control over it at all.

Does that seem sensible?

I'm just hoping Space Cat is wrong, another £50 on a programmer doesn't seem like a good idea!

 

[electronicsuk]

It now doesn't come on at all, until I turn the thermostat up until it clicks. However the programmer seems to have no control over it at all.

Are you saying that you can turn the heating on/off via the stat, but if the stat is set low (i.e. it is on) and then you try and turn the CH off by the programmer, it stays on?

If that seems to be the case, I can only suggest you meter across terminals 1 and 4 with the CH on at the programmer and see if you get 230v, then turn off at the programmer and check there is no voltage between the same two terminals.

If you measure voltage regardless of the setting on the programmer then you have probably knackered this programmer too, as you say you do have control over the heating via the stat.

 

[Lectrician]

You have most deffenantly welded the contacts inside the programmer shut! It is damaged, and should again be replaced.

You would be better getting someone inthe know to sort this for you if you do not want to run the risk of frying another.

HOWEVER, it does sound like you h ave sorted the stat, and if the stat truely is turning the heating on and off without blowing any fuses, then you would be safe to swap over the programmer for a new one.

Sorry to say again, but you most deffenantly have frazzled the controller.

 

[Handaloo]

Ok, well I'm going to get a replacement programmer from my supplier anyway, they've agreed to let me try another and they'll send this one back.

Lectrician - I hope you're right, I'll be leaving as is until I get the new programmer, then we'll see what happens!

I take it that is conclusive? There is no way that the way it is behaving now could be due to the wiring being incorrect?

Electronics UK wrote:

Are you saying that you can turn the heating on/off via the stat, but if the stat is set low (i.e. it is on) and then you try and turn the CH off by the programmer, it stays on?

Yes in a way, no matter what the thermostat is set to, the programmer doesn't do anything to the heating, however, when I click the thermostat on to around 15 degrees, it the heating then comes on, but the programmer still doesn't respond, to either turning it off, or on again.

So in conclusion, how it was wired in at the beginning of this post caused it to be on constantly, and now the programmer doesn't control it full stop.

Annoying.....

Thanks everyone for the help tho, it is massively appreciated.

 

[Space cat]

You say that the programmer unplugs. Here is a test with a very, very thin chance. Try running it with the programmer unplugged. If the heating still comes on under thermostat control you can save yourself fifty quid. Your friend has somehow bypassed the programmer. Sadly, I am 99.9% sure that it will not work like this. You'll be another £50 down.

Meanwhile, you still cannot be sure that the thermostat is wired correctly. You have blue (neutral) in the right terminal because you are no longer blowing fuses. You also have red and yellow in the right terminals - but not necessarily in the right order! One of those two wires is live feed in from the programmer and should go to terminal one. The other is switched live out and goes in terminal two. You have no idea which of those two wires is which. The thermostat will appear to work if you cross them over but regulation will be poor and the temperature will not come up to the set level.

Find the wire which is always live when the programmer is asking for heat. That one is live feed in and it should be on terminal one. The other will be live only when the thermostat is also asking for heat.

PS: I strongly recommend that you get this sorted out BEFORE you replace the programmer!

 

[MANDATE]

I have to agree with space cat, you really must establish which is the 'live' red or yellow to make sure it functions as it was designed to do so.
Regarding your programmer, it is nothing more than a time operated switch. The heating is controlled by the room stat but can only do that using the power supplied from the programmer.
The 'live' going into the room stat is only 'live' when programmer switches it on.
If you test this and it is still 'live' after programmer has switched if off, then programmer is faulty (or wired incorrectly).
A £5 test meter from Maplins is worth its weight in gold.

 

[Handaloo]

Ok,

I've bought myself a power tester. and here are the results.

When touching the neutral and the yellow wire in terminal 1, there is no current. when doing the same with neutral and red in 2, there is. This doesn't change when I turn the heating on from the programmer. However it does change, when I turn the heating on from the thermostat.

I take it this means the programmer is KAPUT?

Also, Space Cat, you were right, the programmer being removed means nothing works. So it was a thin chance indeed.

 

[MANDATE]

OK now you know 'yellow' is switched live so terminal 2 it is! 'red' is permament 'live' so terminal 1.
You say it does not change when when heating turned on from programmer. That presumes it was in the off position when you tested and none of the wires should be live.
If the programmer was functioning correctly, turning the CH off would remove the power from the 'red' wire,
As the programmer has no effect, then it must be faulty (unless wired wrong and the switch is being by passed).

 

[Handaloo]

Dear All,

Just to let you know, I got the new programmer today (exchanged it, saved myself £50!) and it works spot on.

So thanks again for all your help!

Andrew

 

[Space cat]

It's nice to get some positive feedback (except in control systems ) but ---.

exchanged it, saved myself £50!

Let's hope that the supplier doesn't read this thread!

Space Cat over and out.