Connecting a wifi thermostat for central heating

[joddle]

We have a property with a combie boiler for hot water and central heating. The CH is simple enough running from the boiler through the house to a rad in each room and it is controlled by a simple thermostat in the lounge. However we are often away and would like to activate the heating remotely so am thinking of using a wifi thermostat - the only issue being that the current thermostat is battery powered and only has a two wire cable to the boiler which is some distance away. Changing that cable would not be easy due the construction of the house.

As I understand it, normally a 3 wire cable is needed so it can provide power to the thermostat as well as returning power to the boiler to activate it. However we do have a mains socket directly next to he thermostat so is there any type of wifi thermostat which can use the existing two wires to control the boiler but be powered independently from the nearby socket? The house is all on a single phase.

 

[winston1]

As you are in the UK I suggest you post this in the electrics UK forum.

 

[joddle]

As you are in the UK I suggest you post this in the electrics UK forum.

But the house concerned is in Spain. I used to live in Sussex (and still have a house there) so needed to change my details which I have now done - sorry for the confusion.

 

[FrodoOne]

We have a property with a combie boiler for hot water and central heating. The CH is simple enough running from the boiler through the house to a rad in each room and it is controlled by a simple thermostat in the lounge. However we are often away and would like to activate the heating remotely so am thinking of using a wifi thermostat - the only issue being that the current thermostat is battery powered and only has a two wire cable to the boiler which is some distance away. Changing that cable would not be easy due the construction of the house.

You wrote "the current thermostat is battery powered and only has a two wire cable to the boiler."

I believe that you will find that the thermostat is actually powerd by a 24 V (AC) supply "from the boiler" and this supply is rectified and "dropped" to a suitable voltage for the thermostat and the battery is only a "back-up" - for time keeping purposes.

If this is the case, you could search on "24V WiFi Thermostat"

However, it would probably be better still if you went straight to https://yourhome.honeywell.com/en/Products/Wi-Fi-Thermostats
On this site you will find that you can work through to "Guides" (such as https://customer.honeywell.com/resources/techlit/TechLitDocuments/33-00000s/33-00269EF.pdf), which will tell you how to check that which you have and what you need to do to replace your existing thermostat. (Note the need for a "C" wire.)

Many of these thermostats can control more "systems" than the simple one that you have but (if it IS 24 V), they will all do that which you seem to require.

 

[joddle]

You wrote "the current thermostat is battery powered and only has a two wire cable to the boiler."

I believe that you will find that the thermostat is actually powerd by a 24 V (AC) supply "from the boiler" and this supply is rectified and "dropped" to a suitable voltage for the thermostat and the battery is only a "back-up" - for time keeping purposes.

If this is the case, you could search on "24V WiFi Thermostat"

However, it would probably be better still if you went straight to https://yourhome.honeywell.com/en/Products/Wi-Fi-Thermostats
On this site you will find that you can work through to "Guides" (such as https://customer.honeywell.com/resources/techlit/TechLitDocuments/33-00000s/33-00269EF.pdf), which will tell you how to check that which you have and what you need to do to replace your existing thermostat. (Note the need for a "C" wire.)

Many of these thermostats can control more "systems" than the simple one that you have but (if it IS 24 V), they will all do that which you seem to require.

The 24v idea does not seem to fit with what we have got. The twin cable from the boiler is not 24v. the wires seem simply to connect the supply to the boiler. Shorting them activates the boiler, disconnecting them de activates it. It could be replaced by a simple bi-metal strip thermostat which is in effect a switch. I believe the 24v systems are used in other countries but not here.

 

[FrodoOne]

The 24v idea does not seem to fit with what we have got. The twin cable from the boiler is not 24v. the wires seem simply to connect the supply to the boiler. Shorting them activates the boiler, disconnecting them de activates it. It could be replaced by a simple bi-metal strip thermostat which is in effect a switch. I believe the 24v systems are used in other countries but not here.

What is the make and model of the thermostat? Does it have "timing" functions?
What are the 2 wires used between it and the "Boiler" (Are they insulated for 230 V AC or are they control/signal/"telephone" insulated wires?)
Have you measured the voltage applied?

If the thermostat "could be replaced by a simple bi-metal strip thermostat", it is MOST unlikely to be operating on 230 V.

Since it is "a combie boiler for hot water and central heating", the wall thermostat must be controlling a valve to turn on the Central Heating and the "boiler's" own thermostat regulates the temperature of the hot water in the "boiler".
While it is possible that this is 230 V wiring, I believe that it would be unusual to allow a 230 V connection to a device such as a thermostat containing a back-up battery.

 

[joddle]

Seems very possible it is 240v - just found the manual. The cable between the boiler and thermostat is mains cable double insulated. The hot water is direct so is not controlled from the thermostat at all. There is a simple hot water temp control on the boiler - turning the tap on activates the hot water. The thermostat only controls the central heating. The wiring diagram shows two possible modes of wiring but I have no idea which is used on our boiler which is a Vailant about 6 years old. The thermostat is a Cepra 5300. Will have to look closer next time I am there.

 

[FrodoOne]

Seems very possible it is 240v - just found the manual. The cable between the boiler and thermostat is mains cable double insulated. The hot water is direct so is not controlled from the thermostat at all. There is a simple hot water temp control on the boiler - turning the tap on activates the hot water. The thermostat only controls the central heating. The wiring diagram shows two possible modes of wiring but I have no idea which is used on our boiler which is a Vailant about 6 years old. The thermostat is a Cepra 5300. Will have to look closer next time I am there.

I found the manual for that thermostat and on page 36 of the (English) installation instructions I found the diagram indicating (indeed) a 230 V control connection.

Looking at available thermostats which could be substituted for this, I found the Salus iT500 Internet Thermostat.
If you go to http://www.salus-tech.com/downloads/ and download SALUS-iT500-Manual.pdf, on Page 12 you will find the connections for what they term "Volt Free - Combination Boiler"

If you disconnect the existing wires from the existing thermostat and place them on the COM and NO terminals of the iT500 it should control you boiler as required. These connections are shown in BLACK - and marked 0V. (The "Line" side should go to the COM terminal but it wont really matter.)

This should work with the either of the set-ups shown on the Cepra 5300 diagram.

Of course, you will ALSO need to supply 230 V from your nearby outlet to the L an N terminals of the iT500

There may be other Thermostats which could be used but this was the first one that I found.

I hope that this is of some help to you.

 

[joddle]

I found the manual for that thermostat and on page 36 of the (English) installation instructions I found the diagram indicating (indeed) a 230 V control connection.

Looking at available thermostats which could be substituted for this, I found the Salus iT500 Internet Thermostat.
If you go to http://www.salus-tech.com/downloads/ and download SALUS-iT500-Manual.pdf, on Page 12 you will find the connections for what they term "Volt Free - Combination Boiler"

If you disconnect the existing wires from the existing thermostat and place them on the COM and NO terminals of the iT500 it should control you boiler as required. These connections are shown in BLACK - and marked 0V. (The "Line" side should go to the COM terminal but it wont really matter.)

This should work with the either of the set-ups shown on the Cepra 5300 diagram.

Of course, you will ALSO need to supply 230 V from your nearby outlet to the L an N terminals of the iT500

There may be other Thermostats which could be used but this was the first one that I found.

I hope that this is of some help to you.

Many thanks for that - you have really answered my initial query and in doing so have also explained how it would all work. I can now go ahead