You turned on the hot water and the water heater Ariston or Hotpoint Instead of the usual heating, it displays a mysterious error on the display H20? Do not rush to call a specialist - in 80% of cases the problem is solved on its own in 10–30 minutes. This error is one of the most common in the boiler line. Ariston, but its meaning is often misinterpreted. We'll figure out what code H20 does not indicate a breakdown of the heating element or thermostat, but problems with the water supply or pressure in the system, and we will explain in detail how to return the water heater to operation.

In this article you will find:

  • 🔍 Exact value of error H20 and why it appears (spoiler: it's not always a malfunction!).
  • 🛠️ Step by step instructions for diagnostics - from checking the tap to testing the check valve.
  • 💡 Remedies for different models (Ariston ABS VLS EVO PW 50, Hotpoint-Ariston SG 30 OR etc.).
  • ⚠️ What to do if an error is returned - when you can’t do without a master.

What does error H20 mean on an Ariston boiler?

Code H20 (sometimes shown as H02 or E20 on older models) is deciphered by the manufacturer as "no water in tank" or "insufficient inlet pressure". This not an electronic failure, but a signal that the boiler cannot start heating due to:

  • 🚰 Shut off water supply — they forgot to open the tap, the valve on the pipe jammed.
  • 🔧 Clogged filter at the inlet or check valve.
  • 💧 Low pressure in the system (less than 0.5 bar) - relevant for upper floors or in case of accidents at the water utility.
  • 🔄 Air lock in pipes after draining water or repairs.

Important: error H20 may appear even with visually working water supply For example, if the pressure at the inlet to the boiler has dropped to 0.3 bar (the norm is 1.5–3 bar), and water is still flowing at the kitchen faucet. In this case, the boiler blocks heating to avoid overheating of the heating element.

📊 How often do you encounter water heater errors?
First time
Once a year
More often than 2 times a year
Something is always breaking

First steps: what to do with error H20?

Before disassembling the boiler or calling for service, perform basic check — in 60% of cases the problem is solved in 5 minutes:

Check if the cold water tap at the boiler inlet is open

Make sure that the pressure in the system is not lower than 0.5 bar (look at the pressure gauge or open any tap in the house)

Click the button RESET on the control panel (if available)

Try draining 1-2 liters of water through the hot water tap - this will help bleed out the air-->

If after these steps the error disappears, the problem was in temporary failure. But if the code H20 appears again, proceed to detailed diagnostics.

⚠️ Attention: On models Ariston ABS PRO ECO PW 80 and Hotpoint-Ariston SG 50 OR after resetting the error you may need manual heating start - press and hold the button POWER 3 seconds.

Checking water pressure: standards and solutions

Boilers Ariston require minimum pressure 0.5 bar at the input, and for stable operation - 1.5–3 bar. If the pressure is lower, protection is triggered and H20. Here's how to check and fix:

Problem How to diagnose Solution
Low system pressure Open the cold water tap all the way - low pressure? Install booster pump (for example, Grundfos UPA 15-90).
The coarse filter is clogged Look at the filter mesh - is there any rust or debris? Rinse the filter under running water or replace it.
Check valve faulty Is water dripping from the boiler when the hot water tap is closed? Replace the valve (cost - from 300 ₽).
Air lock Do you hear gurgling sounds when you open a hot water tap? Bleed air through a tap or safety valve.

For accurate pressure measurements, use pressure gauge (connects to the fitting at the boiler inlet). If the pressure is consistently low, contact the management company - the problem may be in the house pipes.

💡

If your water is often turned off, install hydraulic accumulator for 24–50 liters. It will maintain pressure in the system and protect the boiler from error H20.

Cleaning the filter and check valve: step-by-step instructions

Clogged filter or valve - cause 30% of cases errors H20. Cleaning takes 15–20 minutes and does not require special tools. Here's how to do it:

  1. Shut down cold water tap at the entrance to the boiler.

  2. Unscrew coarse filter (located in front of the check valve) using a wrench. Inside you will see a mesh - rinse it under pressure of water.

  3. Check check valve (plastic or brass element with a spring). Click on its flag - if the water does not flow or flows weakly, the valve is clogged.

  4. Remove the valve, disassemble (if possible) and wash. If the spring is rusty or deformed, replace the valve.

  5. Reassemble everything in reverse order, open the tap and check if the error disappears.

⚠️ Attention: On models Ariston LYDOS R and Hotpoint-Ariston CLS 30 The non-return valve is built into the safety block. Do not try to disassemble it - just replace it!
How to distinguish a clog from a broken valve?

If after cleaning the valve still does not allow water to flow through or flows in the opposite direction (water flows from the boiler when the hot water tap is closed), it needs to be replaced. The price of a new valve is from 200 to 800 rubles, depending on the model.

Electronics problems: when is the pressure sensor to blame?

If mechanical causes are excluded and the error H20 remains, the problem may lie in:

  • 📶 Pressure sensor (pressostat) - it gives a false signal about low pressure.
  • 🔌 Control board — firmware failure or contact oxidation.
  • 🔋 Boiler power supply — power surges could throw off the settings.

For diagnostics:

  1. Unplug the boiler for 5 minutes, then turn it on again. If the error disappears, a temporary glitch is to blame.

  2. Check pressure sensor contacts (usually located on the inlet pipe). Clean oxidized contacts with sandpaper.

  3. If after switching on the boiler immediately shows H20, but there is water - sensor is faulty. Replacing it will cost 1,200–2,500 rubles.

On models Ariston Velis Evo WiFi the failure may be due to firmware. Try resetting to factory settings:

Press and hold the button MODE 10 seconds → the boiler will beep → release the button.

Error H20 after draining the water: how to bleed the air?

If you have recently drained water from the boiler (for example, to clean the heating element), the system may have formed air pocket. It blocks water circulation and causes error H20. To clear a blockage:

Open the hot water tap to maximum

Wait 2-3 minutes - there should be jerks of water and air

If this doesn’t help, unscrew the hot water hose from the boiler and drain 1-2 liters (substitute a bucket!)

Close the tap, connect the hose back and check the operation-->

On vertical models (Ariston ABS VLS INOX PW 100) air accumulates at the top of the tank. In this case:

  1. Turn off the cold water supply.

  2. Open safety valve (it has a lever) and drain 5-10 liters of water.

  3. Close the valve, turn on the water supply and start the boiler.

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If error H20 appears again after bleeding the air, check tightness of connections — perhaps air is being sucked in somewhere.

When to call a professional: signs of serious damage

In most cases the error H20 can be eliminated on your own, but there are symptoms for which it is better to contact the service:

  • 🔥 The boiler is electrocuted or the RCD is triggered when turned on.
  • 💦 Water is leaking from under the lid - a sign of damage to the tank.
  • 🔊 Loud noise or whistling when heating (may indicate a malfunction of the heating element).
  • 📉 Error H20 appears even with normal pressure and clean filters.

Service repair cost:

Problem Repair price (₽)
Replacing the pressure sensor 1 500–2 800
Cleaning the tank from scale 2 500–4 000
Replacing the control board 4 000–7 000
Tank leak repair From 5,000 (if possible)
⚠️ Attention: If the boiler is under warranty, don't disassemble it yourself - this will void the warranty. Contact an authorized service center Ariston.

FAQ: Frequently asked questions about the H20 error

Is it possible to use the boiler if it shows H20?

No. Error H20 blocks heat so the water stays cold. In addition, ignoring the problem can lead to overheating of the heating element and its failure.

Why does error H20 appear at night and disappear during the day?

Most likely at night water pressure drops (for example, due to massive water consumption in the house). Install pressure reducer or a hydraulic accumulator to stabilize the pressure.

How to reset error H20 on Ariston ABS VLS INOX?

Press and hold the button RESET (or MODE + +) for 5 seconds. If there is no button, unplug the boiler for 1 minute.

Can error H20 occur due to scale?

Indirectly - yes. A strong layer of scale on the heating element reduces heat transfer, and the boiler may falsely trigger for overheating, blocking heating. But H20 does not cause scale.

What should I do if the error remains after replacing the check valve?

Check:

  • Correct installation of the valve (the arrow on the body should indicate towards the boiler).
  • Pressure in the system (perhaps the problem is not in the valve, but in low pressure).
  • Integrity of hoses (no kinks or blockages).