Domakihub Adjust Your Electric Water Heater Thermostat Safely
Fix lukewarm water yourself by accessing the hidden thermostat dials inside your storage boiler — no technician needed.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 4 min read
If your shower runs warm but never hot, or your holiday rental guests keep complaining about lukewarm water, the fix is almost always a thermostat adjustment hidden behind the boiler's access panels — not a broken heating element. The video above walks through the full procedure with a master plumber, and the steps below give you a precise, safety-first sequence you can follow in any Greek home, rental property, or small hotel. A few minutes with a screwdriver is all it takes.
Why the Thermostat Gets Out of Range
Electric storage boilers (known locally as thermosifono) ship from the factory with the thermostat set conservatively — often between 49 °C and 54 °C — to reduce standby energy use and limit liability for scalding. In a holiday rental that sits empty for weeks, or after a power surge, that dial can drift or simply need raising to meet actual hot-water demand.
In Greece, incoming cold water from uninsulated roof tanks can be considerably cooler in winter, which means a setting that felt adequate in July becomes noticeably lukewarm by November. Rather than running the boiler longer and paying more in electricity, the smarter fix is to set the thermostat to the right temperature once.
Safety Before You Open Anything
An electric water heater operates at mains voltage. The single non-negotiable rule is to cut power at the circuit breaker before you remove any access panel. Confirm the power is off with a non-contact voltage tester held near the element leads — do not rely on the boiler's indicator light alone, as it may stay lit briefly after shut-off.
Most Greek boilers have two access panels: one at the top for the upper thermostat and element, and one at the bottom for the lower pair. Both compartments contain live wires when energised, and both must be de-energised before you touch anything. Keep a dry towel nearby; small amounts of condensation around the panels are normal.
How to Adjust the Thermostat Step by Step
- 1
Cut power at the circuit breaker
Locate the dedicated breaker for the water heater in your distribution panel — it is usually a double-pole 16 A or 20 A breaker labelled 'boiler' or 'water heater'. Switch it off, then confirm no voltage is present by holding a non-contact tester near the boiler's supply cable before touching any panels.
- 2
Remove the access panel cover and insulation
Unscrew the rectangular cover plate on the front of the boiler using a flathead or Phillips screwdriver. Behind it you will find a layer of insulating foam or fibreglass blanket tucked over the thermostat assembly. Carefully pull this aside and set it somewhere dry — you will need to replace it exactly as found to maintain the boiler's energy rating.
- 3
Locate the thermostat dial and read the current setting
The thermostat is a small dial or slider, often red or white, mounted against the side of the tank. A reference arrow or notch indicates the current set point on a scale from roughly 'warm' (around 40 °C) to 'hot' (up to 75 °C). Note the existing position before you move anything so you can return to it if needed.
- 4
Set the dial to the recommended temperature
For a primary residence or rental property, turn the dial to 60 °C. This temperature is hot enough to eliminate Legionella bacteria (which thrive between 20 °C and 50 °C) while remaining safe for normal use when mixed with cold water at the tap. For a hotel or property with children, confirm local water-safety requirements first — some jurisdictions mandate a minimum of 60 °C at the cylinder. Use a flat-blade screwdriver to turn the dial if it is recessed.
- 5
Replace insulation and panel, restore power, and verify
Tuck the insulation blanket back into place exactly as it was, re-fit the panel cover, and tighten the screws snugly but not over-torqued. Restore power at the breaker and allow the boiler 45–90 minutes to reheat fully before testing at a tap. If the water now reaches the target temperature and the boiler cycles off normally, the job is done. If it still runs lukewarm after a full heat cycle, the element may need professional inspection.
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FAQ
- What temperature should I set my electric water heater thermostat to in Greece?
- 60 °C is the standard recommendation for homes and rental properties. It is hot enough to prevent Legionella bacteria growth and provides comfortably hot water when mixed at the tap, while avoiding unnecessary energy waste that comes with settings above 65 °C.
- My boiler has two access panels — do I need to adjust both thermostats?
- Most storage boilers have an upper and a lower thermostat controlling separate heating elements. The upper thermostat is the primary one and handles the bulk of the heating cycle; the lower thermostat provides additional capacity during high-demand periods. Set both to the same temperature so the heating is consistent throughout the tank. The procedure is identical for each panel.
- How long does it take for the water to heat up after I adjust the thermostat?
- A standard 80-litre to 120-litre boiler common in Greek properties takes roughly 60 to 90 minutes to heat a full tank of cold water at 60 °C. If the tank is already partially warm, you may have hot water in as little as 30 minutes. Avoid testing at the tap until the boiler's indicator light has cycled off, which signals the target temperature has been reached.