Can I rewire my boiler to use a 3 wire thermostat?

[JamesPrice]

I've been looking at replacing the old thermostat in my house with one of the Heatmiser ones - either the PRT-TS or if I'm feeling flush the wifi version. Both say they require a 3 wire connection + earth.

My present thermostat is 2 wire.

I have a glow-worm flexicom 24cx boiler. Can I rewire the boiler and switch unit to give me a 3 wire connection for the Heatmiser thermostats?

Thanks for the help. I'll post a diagram of the boiler wiring in a sec, can't seem to do it from my phone. System upgrade DIYnot?

 

[JamesPrice]

Glow-Worm Flexicom 24CX wiring 230V

• JamesPrice
• 4 Mar 2012
• 1

 

[plumbplumb]

i presume by 3-wire you mean

Common
Switch Live
Neutral

If so then wire Neutral to Neutral in the boiler.
Common on the room stat to boiler live
Switch live on the boiler to to R

removing the link between Live and R

 

[Agile]

Warning to DIYers.

This boiler has both low voltage ( 24v ) AND 230v ac control connections which give great flexibility for the installer.

Some boilers only have 230v controls.

But some other boilers only have low voltage controls. If anyone connected 230v to those then it would destroy the boiler PCB which is an expensive part.

Tony

 

[JamesPrice]

Thanks for the swift replies. The Heatmiser website just says:

"*Three wires, excluding earth, is required for this thermostat"

http://www.heatmisershop.co.uk/epag.../Heatmiser/Products/"PRT-TS (EU)"/SubProducts

It sounds as though that'll probably be the three wires you mention, but is there some way for me to make sure?

Cheers!

 

[matt1e]

the heatmiser needs a live and neutral for it to work, which is two of the cores
you can pick this up from the boiler or wiring centre

then you have to decide if you are going to use 230v or voltfree switching
you will need a third core for 230v
or a third and fourth core for voltfree

you will also need to answer these questions
how is the boiler switched at present? a photo of the boiler connections will help
do you have any zone valves?
and are they 2 or 3 port?

Matt

 

[JamesPrice]

Thanks all,

I've just opened up the electrics for the first time to find it's wired up to the 24v system controls so I guess I posted the wrong diagram before. Photos and other diagram coming up shortly.

I can use the touch screen Heatmiser above with 24v can I?

Thanks for being so helpful!

 

[JamesPrice]

Glow-Worm Flexicom 24CX wiring 24V

• JamesPrice
• 4 Mar 2012
• 1

Glow-Worm Flexicom 24CX wiring interior

• JamesPrice
• 4 Mar 2012
• 1

Glow-Worm Flexicom 24CX wiring boiler switch

• JamesPrice
• 4 Mar 2012
• 1

 

[vicvapour]

the heatmiser needs a live and neutral for it to work, which is two of the cores
you can pick this up from the boiler or wiring centre

then you have to decide if you are going to use 230v or voltfree switching
you will need a third core for 230v
or a third and fourth core for voltfree

you will also need to answer these questions
how is the boiler switched at present? a photo of the boiler connections will help
do you have any zone valves?
and are they 2 or 3 port?

Matt

Outputs: Volt free 3A Max

 

[matt1e]

the heatmiser needs a live and neutral for it to work, which is two of the cores
you can pick this up from the boiler or wiring centre

then you have to decide if you are going to use 230v or voltfree switching
you will need a third core for 230v
or a third and fourth core for voltfree

you will also need to answer these questions
how is the boiler switched at present? a photo of the boiler connections will help
do you have any zone valves?
and are they 2 or 3 port?

Matt

Outputs: Volt free 3A Max

your point Vic?

 

[matt1e]

Thanks all,

I've just opened up the electrics for the first time to find it's wired up to the 24v system controls so I guess I posted the wrong diagram before. Photos and other diagram coming up shortly.

I can use the touch screen Heatmiser above with 24v can I?

Thanks for being so helpful!

yes you can Jim but whether you need a 3 core or 4 core (plus earth) to it will depend on your system
you also need to assertain how the boiler is controlled
ie via stat or via zone valve
it is much more likely to be the latter
so have a look for any of these

and if you have one of these or similar

take the cover off and post a pic of the connections

Matt

 

[JamesPrice]

Thanks Matt

No sign of those in my flat. It's only 74m sq in area (central london innit) so I think variation between the rooms is just controlled by dials on the radiators. My bills are pretty low so I'm not sure it'd be worth installing any zone controls. I can buy some 1.5mm sq 3 core & earth from round the corner.

 

[matt1e]

3 core and earth is no use to you mate as you will need 4 core and earth
so either run another twin & earth from the spur to the new stat along with the twin already there or replace the existing twin and earth with 4 core and earth

Glow-Worm Flexicom 24CX wiring boiler switch

• JamesPrice
• 4 Mar 2012
• 1

you need to connect the line and neutral on the new stat to the load side of the spur (in with the brown and blue allready connected to it)
A1 and A2 on the new stat will connect to the connector block shown inside the spur back box (doesnt matter which way around)

if it is easier to run a new cable to the stat from the boiler then do that

Matt