Domakihub Install an Instant Hot Water Tap in 5 Simple Steps
Get near-boiling water on demand without waiting — here is how to fit one yourself.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
An instant hot water tap delivers near-boiling water the moment you turn it on, cutting the wait for kettles or immersion heaters — a real advantage in a busy Greek rental villa, hotel kitchen, or family home. The video above walks through a complete installation on a real sink; this guide gives you the ordered steps, tool list, and safety notes so you know exactly what to expect before you start. Most competent DIYers can complete the job in two to three hours, though in Greece a licensed plumber is strongly recommended for the final water connections.
What is an instant hot water tap?
An instant hot water tap — sometimes called a boiling water tap or hot water dispenser — connects to a dedicated under-sink tank (typically 2–4 litres) that keeps water at around 98 °C at all times. When you open the tap, pressurised hot water flows immediately with no heating delay.
Most modern units are sold as a 3-in-1 system: a single tap head delivers filtered boiling water, regular hot water, and cold water. This is different from a simple electric tap that heats water in the spout — the under-sink tank gives you true instant delivery at volume, which is useful for tea, pour-over coffee, blanching vegetables, or sanitising surfaces in a holiday apartment.
What you need to know before you start
Check that you have a spare 13 A earthed socket (or a 16 A circuit in older Greek installations) within reach of the under-sink cabinet — the tank draws 1.5–3 kW and must not run from an extension lead. You also need cold-water supply access under the sink; most kits include a saddle valve or T-piece that taps into the existing cold-water pipe without draining the whole system.
Greek properties often use 3/8-inch or 1/2-inch compression fittings, which are compatible with the flexible hoses included in most European tap kits. If your building has a pressurised supply above 6 bar, fit an inline pressure reducer before the tank — most manufacturers specify a maximum of 5–6 bar.
How to install an instant hot water tap
- 1
Gather tools and prepare the workspace
You will need an adjustable spanner, basin wrench (for reaching up inside the cabinet), PTFE tape, a drill with a 35 mm hole-saw bit (if your sink has no spare hole), a bucket, and a cloth. Shut off the cold-water supply at the isolation valve under the sink or at the mains stopcock. Open the existing tap to release pressure and drain residual water into the bucket.
- 2
Mount the tap head through the sink deck
If there is an existing blank hole in your sink deck, remove the plug. Otherwise drill a 35 mm hole at least 80 mm from the existing tap. Feed the flexible supply hoses down through the hole, place the decorative collar over them, then secure the mounting nut underneath with a basin wrench — firm but not over-tightened on a ceramic or composite sink, as cracking is a real risk. Some 3-in-1 taps have separate hot and boiling inlets, so note which hose is which before you proceed.
- 3
Install the under-sink tank
Position the insulated tank on the back wall or floor of the cabinet; most units come with a bracket. Connect the cold-water inlet on the tank to the cold supply using the saddle valve or T-piece supplied — wrap all male threads with two or three turns of PTFE tape before making up the joint. Attach the hot-water outlet hose to the tap's hot inlet, and — if it is a 3-in-1 unit — connect the boiling outlet hose to the tap's boiling inlet. Leave all connections hand-tight until you have confirmed the routing is correct.
- 4
Make the electrical connection
Plug the tank's power cable into the dedicated earthed socket — do not switch it on yet. In Greece, if the socket is not already present, have a qualified electrician add one; working inside a consumer unit yourself is not permitted under national electrical regulations (ΦΕΚ regulations for electrical installations). Once everything is wired, double-check that the power switch on the tank is in the OFF position.
- 5
Commission and test the system
Slowly reopen the cold-water supply valve and check every joint for drips — tighten any that weep, then switch on the tank and allow it to fill and heat for the time specified in the manual (typically 5–15 minutes). When the indicator light shows ready, test the cold-water flow first, then hot, then the boiling function. Hold a cup under the boiling spout before operating it — the child-safety mechanism on most taps requires a push-and-turn action. If any joint drips under live pressure, shut the supply, dry the joint, add PTFE tape, and remake it before re-pressurising.
Rather have a pro handle it?
Get a vetted plumbing pro in your city — one number, booked in EN/EL/DE.
FAQ
- Do I need a plumber to install an instant hot water tap in Greece?
- Greek law does not ban a homeowner from making minor plumbing connections to an existing supply pipe, but most manufacturers' warranties require installation by a certified tradesperson. For rental properties (holiday villas, AirBnB units) you also need documented maintenance records, so hiring a licensed plumber is strongly advisable — and on Domakihub you can find vetted plumbers in your area.
- How much electricity does the under-sink tank use?
- A standard 2.5-litre tank draws roughly 1,500–2,000 W to heat up initially, then cycles on and off to maintain temperature, averaging around 0.2–0.5 kWh per day in a household setting. Switching the tank off overnight or when the property is empty between rentals cuts this by around 30–40%.
- Can I connect an instant hot water tap to filtered water?
- Yes — most 3-in-1 boiling water taps include an inline carbon filter that removes chlorine taste and limescale from the boiling circuit. In areas of Greece with hard water (Attica, many island municipalities), fitting a compatible filter cartridge is strongly recommended; limescale build-up in the tank reduces efficiency and can void the warranty within months if left untreated.