Home heating automation
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Grants are a honeytrap. Installers just up their prices to adsorb them.
Connecting the boiler call wires, aka the call for heat, the switched live (SL), or just a volt free relay normally open contact pair are all names for roughly the same thing. Connection to the electrical terminals inside the boiler cover is a simple task. There's nothing particularly expert or hazardous about doing this (though there's an English sparks on YouTube who was nearly fried because this connection was done by... the RGI.) Any technically qualified electrician, electrical technician, engineer, or plumber/gas installer with basic domestic mains training would know what he's doing. One important thing is that the live being sent to call the boiler via its SL terminal, should come from the same breaker as the permanent live which powers the boiler. If using the wireless relay, the live into this should be from the same source, and after the boiler wall switch. In many instances the live is just fed out of the boiler to the relay volt free terminals and back to the call for heat or SL terminal, which is the safest setup.
The hazard I mentioned on the YT channel occurred when the YT sparks isolated the kitchen mains to do some alterations, but the boiler SL was coming from an upstairs hot press circuit that wasn't turned off. This fed through the boiler SL terminal and back out through its isolated mains neutral connection, leaving quite a tickle on the wires which had been isolated from the main.
Replacing the timer with the EPH receiver will safely replicate exactly the same wiring which is already there, and you'll have both Live and Neutral to power the EPH, as well as the SL via it's relay to call the boiler. A really simple job for a sparks, as is the wiring of the zone valves to the Tado extension kit controller. This is made easier by using this little wiring centre box to terminate and link the wires from the zone valves, the Tado control and the SL out to a boiler or the EPH wireless TR1link. Its just a terminal strip with 12 invidual terminals.
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If you don't already have one, a cylinder stat is a €20 device with 20 minutes installation, which will interrupt the timed HW event when the cylinder reaches a set temperature at a fixed point, say, 60° and two thirds of the way down the side. As the zone valves are in the hot press, its just a case of sending the HW SL from the Tado receiver via the cylinder stat and back to the HW zone valve. You can set your timer roughly then for time blocks to top up HW.
With modern low loss deep insulated cylinders, there's not much saving in trying to heat HW just prior to demand by using timers. Unused HW will remain hot for far longer than the old days of bare copper cylinders with their 'saggy underpants' lagging jackets! Heres the most common contact cylinder stat in use. It's ideal for foam encased cylinders, you just cut out a little foam square to let it contact the cylinder wall. Heres one from Screwfix, €19.
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This modified TADO S plan diagram covers it. Using the wiring connector box I mentioned earlier, all the connections are made to it. Included is the diversion to a cylinder stat, if you want, from Tado HW NO (Normally open) to 6, to cylinder stat COM, from cylinder stat NO to 8, and from 8 to HW valve Brown to open the valve, and supply SL to the TR1 transmitter. TR1 will also require a fixed Live to power it up.
TR1 requires L, N, and SL. The receiver TR2 is wired in place of your Timer. You can have all the above done and tested before you connect TR2 to fire the boiler. You will see the icons for CH and HW illuminate on the TADO, the valves will open and their indicators (if equipped) will glow. The TR1 and Tr2 will indicate they've received an SL to fire the boiler. If you install a cylinder stat you can twist it up and down to check it closes the valve during a timed HW event. You can check that either valve opening will set off the TR1. Once you're satisfied, the TR2 can be connected in place of the old Timer to fire the boiler.
Your zone valves are probably currently latched open with a little service lever, if they're not powered. This will be released to allow motor control when the valves are wired up. Heres the S-plan and the TR1TR2 wiring.
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