Domakihub Install a Wall-Mounted Electric Water Heater in 5 Steps
A practical installation guide for the compact electric storage boilers common in Greek apartments, holiday rentals, and hotels.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
The compact electric storage water heater — known in Greece as the thermosifono — is a fixture in nearly every apartment, holiday rental, and small hotel on the island. Installing one correctly means getting the bracket, plumbing, pressure relief valve, and electrical connection right in the right order. The video above walks through the full sequence; this article breaks it into five clear steps you can follow alongside it, whether you are fitting a new unit or replacing an ageing one.
Choosing the Right Unit and Location
Wall-mounted electric boilers for residential and short-let use typically range from 10 to 80 litres. A studio apartment or single bathroom can usually get by with a 30–50 litre unit, while a holiday villa with multiple showers needs 80 litres or more. Check the label for the recovery time (the hours needed to reheat a full tank) and make sure the electrical circuit in the property can handle the rated wattage — most Greek-market units draw between 1,500 W and 2,500 W.
Mount the boiler as close as possible to the shower or tap it serves to minimise heat loss in the pipe run. The wall must be solid masonry or reinforced concrete — the unit is heavy when full of water. Avoid positioning it directly above a shower tray or in a location where the pressure relief valve drain cannot reach a floor drain.
Tools and Materials You Will Need
Gather everything before you start: a hammer drill with masonry bits, a spirit level, heavy-duty wall plugs and bolts rated for the boiler's filled weight, PTFE (thread-seal) tape, two flexible braided hoses (one cold, one hot), a pressure relief valve if not supplied with the unit, pipe cutters or an adjustable wrench, a voltage tester, and heat-resistant electrical cable of the correct cross-section (typically 2.5 mm² in Greece for circuits up to 16 A).
In Greece, plumbing fittings are sold in metric sizes but boilers often have BSP (British Standard Pipe) threaded inlets and outlets — 3/4" is the most common. Pick up a pair of reducing bushings if your existing pipework is a different size. A small bucket and towels are essential for catching residual water when disconnecting the old unit.
How to Install a Wall-Mounted Electric Water Heater
- 1
Mark and Fix the Mounting Bracket
Hold the bracket against the wall at the height specified in the manufacturer's instructions — usually high enough to clear the splash zone but still reachable for the anode inspection later. Use a spirit level to confirm it is perfectly horizontal, then mark the anchor points. Drill into solid masonry with a hammer drill, insert heavy-duty wall plugs, and bolt the bracket firmly. Tug it hard before hanging the unit: a 50-litre boiler weighs roughly 65 kg when full, so there is no margin for a loose fixing.
- 2
Hang the Boiler and Connect the Pressure Relief Valve
Lift the boiler onto the bracket hooks — a second pair of hands is strongly recommended for units above 30 litres. Once it is seated and level, locate the pressure relief valve (PRV) port, usually on the cold-water inlet side. Wrap the PRV threads with two to three layers of PTFE tape, screw it in hand-tight, then add a quarter-turn with a wrench — do not overtighten or you risk cracking the valve body. Attach a discharge pipe to the PRV outlet and route it downward to a floor drain or visible point so any pressure release is immediately obvious.
- 3
Make the Cold and Hot Plumbing Connections
The cold-water inlet is always marked with a blue label or the letter C; the hot outlet is red or marked H — never swap them. Wrap the inlet and outlet stubs with PTFE tape and connect your braided flexible hoses, again avoiding overtightening. On the cold-water line, fit an isolating valve (ball valve) immediately upstream of the boiler so you can cut the supply for future maintenance without draining the whole system. Once both hoses are connected, slowly open the cold-water supply and let the tank fill completely — air will escape through the nearest hot tap, which you should leave open until a steady stream of water flows without sputtering.
- 4
Check for Leaks and Verify the PRV
With the tank full, inspect every threaded joint carefully. Run your fingers around each connection and watch for drips over the next five minutes. The PRV should remain closed under normal supply pressure (typically 2–4 bar in Greek municipal networks). If it weeps continuously, your inlet pressure is too high and you need to fit a pressure-reducing valve upstream. A small drip during initial fill as the tank pressurises is normal and should stop once the system stabilises.
- 5
Make the Electrical Connection and Test
Switch off the circuit breaker and confirm with a voltage tester that the supply cable is dead before touching any terminal. Connect the earth (green/yellow), neutral (blue), and live (brown) wires to the boiler's terminal block exactly as shown in the wiring diagram inside the access panel. In Greece, boilers must be on a dedicated circuit protected by a 16 A breaker and an RCD (residual current device) — if one is not already in the distribution board, have a licensed electrician install it before proceeding. Restore power, set the thermostat to 60°C (the recommended minimum to prevent Legionella growth), and allow the tank to reach temperature — most units take 45 to 90 minutes for the first heat-up.
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FAQ
- How long does a wall-mounted electric water heater last in Greece?
- With annual anode-rod inspections and descaling (lime-scale is aggressive in many Greek regions), a good-quality unit typically lasts 10 to 15 years. Skipping anode maintenance is the most common reason tanks fail early through internal corrosion.
- Can I install the boiler myself or do I need a licensed professional in Greece?
- The plumbing connections are straightforward DIY work, but the electrical connection must comply with Greek electrical regulations (ELOT HD 384). If there is no dedicated RCD-protected circuit already in place, the wiring work must be carried out or signed off by a licensed electrician (ηλεκτρολόγος) to be covered by building insurance.
- Why does my pressure relief valve keep dripping after installation?
- A continuously dripping PRV almost always means the cold-water supply pressure exceeds the valve's rated limit (usually 8 bar). Fit a pressure-reducing valve on the main inlet to bring the pressure down to 3–4 bar. If the PRV still drips at normal pressure, the valve itself may be faulty and should be replaced — never cap or block the discharge pipe as a workaround.