Vaillant Boiler Flashing Radiator Symbol: What It Means

On most Vaillant ecoTEC boilers, a flashing radiator symbol means the boiler is heating the radiators right now. It is a status indicator, not a fault. A steady radiator symbol usually means heating is switched on but nothing is asking for heat at the moment. If the symbol is flashing but your radiators stay cold, or the display shows a code starting with F, that is when something needs looking at. Displays differ between models, so check the manual for yours if a symbol does not match what is described here.

What Does a Flashing Radiator Symbol Mean on a Vaillant Boiler?

It means there is a demand for heating and the boiler is working to meet it. On most ecoTEC plus and ecoTEC pro models the symbol flashes while the boiler is running for the radiators.

When your thermostat or timer calls for heat, the boiler starts the pump, lights the burner and sends hot water round the radiators, and the radiator symbol flashes while that happens. When the room reaches temperature and the thermostat switches off, the symbol goes back to steady. So a symbol that flashes on and off through the evening is normal: it simply tracks your thermostat.

The same logic applies to the tap symbol. A flashing tap on a combi means the boiler is heating hot water, usually because a tap is running. On a system or regular boiler it means it is heating the cylinder.

What Do the Other Symbols on a Vaillant Display Mean?

The main symbols tell you what the boiler is doing, not what is wrong. Faults are shown as codes, not pictures.

• Radiator: central heating. Steady means heating is enabled; flashing means it is heating now.
• Tap: hot water. Steady means hot water is enabled; flashing means it is heating water now.
• Flame: the burner is lit. On many models a crossed-out flame means the boiler has stopped because of a fault with the burner, and an F code will usually show as well.
• Spanner: on many models this is a maintenance reminder set by the installer. It does not stop the boiler working.
• Pressure and bar: the system pressure. On many models the figure flashes when the pressure has dropped too low.

If the radiator symbol is missing altogether, heating has been switched off at the boiler, often by someone turning the heating dial or button down to its off position for summer.

What Are Vaillant S Codes, and Are They Faults?

S codes are status codes. They tell you which stage of its cycle the boiler is in, and they are not faults. F codes are the faults.

On many ecoTEC models you can bring up the S code by pressing the information button, marked i. The ones people ask about most are:

• S.00: no demand for heating. The boiler is waiting.
• S.04: burner on, heating the radiators. This is the normal state behind a flashing radiator symbol.
• S.08: anti-cycling. The boiler has just finished a heating run and is waiting a set time before it fires again, which stops it switching on and off too often.
• S.14: burner on for hot water on a combi.
• S.31: heating switched off or in summer mode, or no heating demand from a connected Vaillant controller.
• S.34: frost protection running.
• S.53 or S.54: the boiler is holding off because it has detected too little water flow. These are worth noting, because they often come before a low pressure or circulation fault.

If the display shows an F code instead, such as F.22 or F.28, the boiler has locked out. Our guide to common Vaillant boiler problems explains the codes you are most likely to see, and what F22 means on a Vaillant covers low pressure, the most frequent one.

Why Is the Radiator Symbol Flashing but the Radiators Are Cold?

If the boiler says it is heating but the radiators stay cold, the heat is not reaching them. The boiler may be firing normally while the water is not moving, or it is being sent to the wrong place.

• Low pressure or air in the system: check the gauge. Most sealed systems sit around 1 to 1.5 bar when cold. Gurgling and cold tops to radiators point to air.
• A pump that is not moving water: the boiler may hum or run hot and then stop. An S.53 or S.54 status often goes with this.
• A sticking diverter valve on a combi: the boiler heats but sends the water to the hot water side instead of the radiators. Hot taps may even run warm.
• Closed valves: radiator valves or thermostatic heads turned down, or isolation valves under the boiler left shut after work.
• Sludge: radiators cold at the bottom and slow to warm point to a dirty system restricting flow.

You can check the pressure, top it up if it is low, and bleed radiators. Our no heating troubleshooting guide walks through those checks in order. Anything behind the casing, such as the pump or diverter valve, is work for a Gas Safe registered engineer.

When Does the Display Mean You Need an Engineer?

You need an engineer when the boiler shows an F code that returns after one reset, or when it looks like it is heating and the house is not warming up. A flashing symbol on its own does not need a call-out.

Before you ring anyone, write down what the display shows: the symbols, any S or F code and the pressure reading, plus the model name from the front of the boiler. That tells an engineer a great deal before they arrive. An S.53 that keeps appearing, for example, points them towards flow and pressure before they open the case. It also saves you paying for a visit when the answer turns out to be a thermostat set too low or heating switched off at the boiler.

If you smell gas at any point, stop and treat it as an emergency: turn the gas off at the meter, open windows, avoid electrical switches and call the National Gas Emergency Service on 0800 111 999.