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Ask The Trades › DIY Forum › Electrical Questions › Heatmiser thermostat and a Vokera Compact HE

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Heatmiser thermostat and a Vokera Compact HE (Read 6135 times)

Matt1980

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Heatmiser thermostat and a Vokera Compact HE
Sep 5^th, 2010, 8:29pm

Hi all

Brought a new house in 2007 that had a Vokera Compact He boiler controlled by a Honeywell T6360B thermostat. It was connected via a three-core-and-earth-cable with; Brown to L (Terminal 1), Black to N (Terminal 3), Earth to Earth, and the Grey folded back onto itself.

I wanted to change the thermostat to a programmable unit and as its in a prominent place in our lounge brought a Heatmiser PRTHW. I've tried connecting it; Brown to L, Grey to N, Black to A2; and with Earth not attached. I can't even get the thermostat to turn on.

Any suggestions on if Ive brought an incompatible thermostat or what I need to do or what I can try to get it to work would be very much appreciated.

Thanks

Matt

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Lectrician

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Re: Heatmiser thermostat and a Vokera Compact HE
Reply #1 - Sep 5^th, 2010, 9:32pm

Your Honeywell stat was wired incorrectly anyway.

The neutral, which you must not confuse with a switched live must be connected to terminal 2.

The live 'feed' should be connected to terminal 1 (from programmer CH out).

The switched live to the valve/boiler etc should be connected to terminal 3.

The colours used may differ in your cable - more than likely the brown is the 'feed', but the other two could be transposed. It depends who wired it. You can check the other end.

Your heatmiser is quite different - it should have a constant feed (L + N), not from a programmer really. There is then a pair of contacts which operate. The com is linked to the feed L, and the NO to the switched live. Perhaps I am not looking at the correct heatmiser stat?

I think it is difficult to help as the previous stat appears to have been wired incorrectly........perhaps you can say what the cables connected to the other end.....?

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Matt1980

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Re: Heatmiser thermostat and a Vokera Compact HE
Reply #2 - Sep 5^th, 2010, 10:28pm

Hi Lectrician, thanks for your response.

Took cover off boiler and tried to find how the wires are connected, but couldn't figure out how to get to that part of the boiler. Didn't want to force it as I have a habit of breaking things.

Could you or anyone else confirm if thermostat is suitable because I am still able to return it and I don't want to pay for someone to install it for them to tell me its incompatible.

If its not suitable any recommendations would be gratefully received.

Thanks

Matt

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CWatters

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Re: Heatmiser thermostat and a Vokera Compact HE
Reply #3 - Sep 6^th, 2010, 8:30am

I have heatmiser stats and quite like them. On mine the wiring is as Lectrician describes.

Live - L (and a link between L an A1)
Neutral - N
Switched Live back to the boiler - A2

See "Heatmiser PRT Standard" on page 19..

http://www.heatmiser.co.uk/manual/dt/dt_manual.pdf

I've got a feeling the Honeywell stat is battery powered and will work without a neutral wire (on it's terminal 2). So although you have enough wires in the cable to provide a neutral there may not be one connected at the boiler end. Hence the new stat doesn't power up.

You would expect there to be a neutral somewhere near the boiler so probably not hard to provide one and get the heatmiser going. If you can't check that the answer might be to find another battery powered "two wire" stat that doesn't need a neutral.

« Last Edit: Sep 6^th, 2010, 8:32am by CWatters »

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Matt1980

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Re: Heatmiser thermostat and a Vokera Compact HE
Reply #4 - Sep 8^th, 2010, 12:07am

Just an update.

Although not 100% I think the following is true:

The Honeywell thermostat is a mechanical unit and therefore does not require a permanent live or batteries to operate.

I opened the Vokera boiler and found the wiring block and after looking at the installation information (online) came to the conclusion that I would need to connect the neutral and a further wire to be a permanent live to get the Heatmiser to work (the existing live only being live when the mechanical thermostat calls for heat).

In the belief this would be a lot of work I have returned the Heatmiser and will search for a battery operated thermostat.

A big thanks again to Lectrician and CWatters for your advice.

Matt

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