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I'm trying to convert a Danfoss Set2 to a Horstmann C27.

 

The old unit only does HW or HW+CH while the new one supports independent control of both.

 

Most of the wiring between the valves and the controller is hidden in the walls so I can't trace them and double check what goes where. I assume I need to re-do some wiring but I can't tell what. Also, they use different back plates.

 

Any help?!

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From what I recall when I changed my controller over a few years ago. All of the cables for control etc are standardised colours.

 

All of the stats etc and pump and valve cables should all go into a central terminal block.

 

 

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Can I ask what type of system you have, fully pumped or not, motorised valves, stats etc.

 

It looks like the red wire on term 1 is going out to a boiler feed when t/s is on (gravity hot water?) and the black wire term 4 feeds heating pump via a room stat provided the controller switch is set to HW/CH ?

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On your original there is a live link added which is common to see but the new one looks like its got a built in link. You might want to check and confirm this.

 

The new one shows on and off because you can get motor open and motor closed valves but most domestic valves are motor open and spring return to close them.

 

Just remember that all the time clock is doing is at the on time joining the incoming live to the switched live which is the one going out to your valve.

The thermostat will also interface this live so that when its up to temperature it effectively cuts off the live supply to where ever its going.

Room stat and tank stat do the same just different circuits.

If you have two valves then one will be for heating and one will be for hot water.

 

When the time clock comes on it just sends a live feed to the valve and the valve opens. When it gets to the end of its travel it operates a micro switch. Again all this does is join a live to a switched live which goes to the boiler/pump to come on and heat up with ever circuit that valve is on.

 

Hopefully this explanation will help you look at what you have and understand how it works so you can replace the time clock.

You usually can find a wiring diagram that shows you how to convert from one make of clock to another but this has to assume your original is wired in correctly..

 

Is your time clock faulty or do you have another reason for changing it.

I ask because most problems if the heating/hot water io not coming on are caused by the valves failing. eg the micro switch not being operated due to the valve not fully opening and you can just change the syncron motor if thats failed.

 

Happy to help if you want to ask more mate.

Ex heating engineer

 

This may help if you can follow a wiring diagram

 

http://www.plumbcenter.co.uk/wcsstore7.00.343.53.04/ExtendedSitesCatalogAssetStore/images/products/AssetPush/DTP_AssetPushHighRes/std.lang.all/ti/on/Horstmann_C21-C27_Installation.pdf

Edited by gsexr
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I wouldn't even bother checking valve end switches and whether or not they're wired in. Just wire the red wire in terminal 1 to the new timer connection 3 and the black in terminal 4 to 4 on the new timer. When you power the timer turn heating on by its self, if the boiler fires great, you're done, if it doesn't just take the timer back off and remove the little black jumper at the back of the timer, this will link the heating and hot water.

 

 

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