Nest Heat Link Wiring in UK Homes: Combi, S-Plan, Y-Plan and OpenTherm

• L and N: the 230 V, 50 Hz supply, which every wiring diagram in the guide shows through a 3 A fuse
• 1, 2 and 3: the heating relay, with 1 normally closed (heat satisfied), 2 common and 3 normally open (call for heat)
• 4, 5 and 6: the hot water relay, laid out the same way; both relays are rated 3 A resistive and 1 A inductive
• OT1 and OT2: the OpenTherm pair, 42 V DC at most
• T1 and T2: 12 V DC at 0.15 A to a wall-mounted thermostat, with no polarity; Google says to connect the earth when they are used

• Switched-live and volt-free systems are compatible, both at low current up to 3 A
• High-current systems are not, such as electric radiators or electric underfloor heating, which can draw 16 A or more
• Proprietary serial-bus boiler controls are not compatible, though Google says converters from some boiler makers may let one work
• District heating works only where the home has its own accessible electric valve
• Only the 3rd gen Heat Link switches hot water for a separate cylinder, and no Nest controls an electric hot water tank

• Combi with a wall programmer or receiver: the Heat Link takes its place and the heating relay does the switching; Google offers combi hot water control only over OpenTherm
• Combi with no external controls: the switching would be made at the boiler's own terminals, which a JACK booking leaves to a Gas Safe engineer
• S-plan, with separate heating and hot water valves and a cylinder thermostat: the two relays take the programmer's two switched outputs at the wiring centre
• Y-plan, with one mid-position valve and a cylinder thermostat: the same two relays, wired into the existing wiring centre
• On any of them, the boiler must still switch off when neither heating nor hot water is calling, which Approved Document L calls boiler interlock

• Common (C) and normally open (NO) from the old thermostat, or OT1 and OT2 where it was on OpenTherm; spare cores go into terminal blocks
• Google's UK terms move it beside the boiler when the home has no room thermostat, or has an integrated receiver
• If your old thermostat is missing from Google's table, Google suggests a Nest Pro or the old thermostat's maker
• It cannot control a separate hot water cylinder

• It needs a couple of additional wires to the Heat Link; existing OpenTherm wires from an old thermostat can be reused, though Google advises this only if necessary
• To check a boiler, look for the OpenTherm logo or ask its maker
• The 3rd gen should be installed by a professional, because its Heat Link is connected with high-voltage wires

• There is 30 cm clear on each side of the Heat Link, as the UK guide asks
• A fused supply is there, or can be added as a spur from an existing circuit outside a bathroom
• The power is isolated and proved dead before anything is disconnected
• Once wired, the boiler fires on a call for heat and stops after it

A vetted pro prices your Nest job from the model and your photos, and the JACK app shows that fixed price before you book.

On heating, where the Heat Link goes moves the price most: a 3rd gen Heat Link in place of a programmer on the same wiring is the plainest job, while hot water on a cylinder, an S-plan or Y-plan wiring centre or an old wired thermostat to take out of the circuit adds to it. Anything that must be wired at the boiler itself is left out of the price and handed to a Gas Safe registered engineer.

On doorbells and cameras, power comes first: a battery doorbell or Nest Cam with a good 2.4 GHz signal is the lightest job, a weak bell transformer is swapped on its existing supply, and the Nest Cam with floodlight is priced as electrical work on your outside-light circuit. For a camera high on a gable, your pro can ask another pro on JACK to help through the Pro2Pro feature.

JACK does not sell devices, so the Nest kit is yours to buy. Accessories the job needs, such as a bell transformer, a fused spur or an outdoor junction box, are agreed and added at cost before you book, and so is parking where it has to be paid for. Several devices go on one booking for one fixed price. Prefer to pay for time? As a guide, hourly hire is typically £45–£95 per hour for smart home work and £55–£110 per hour for electrical work, and a full-day handyman booking is a flat £350–£400 for up to 8 hours on site.