Which faults are common on Vaillant boilers?
Vaillant’s ecoTEC range is one of the most widely fitted families of boilers in the UK, as combis, system boilers and heat-only boilers. Its fault codes are precise, which helps, and a large share of them point at the same thing: the water in the system.
Low pressure (F.22). A sealed heating system needs to hold pressure. When it drops too far the boiler shuts down for safety. Topping up through the filling loop usually gets it running, but a system that keeps losing pressure has a leak somewhere, perhaps at a radiator valve, the pressure relief valve or the expansion vessel. Our F22 guide explains how to top up safely.
Circulation faults (F.75 and F.83). The boiler checks that water is moving and warming as expected. Air in the system, a weak pump, a faulty pressure sensor or simply too little water will trigger these. Bleeding radiators and topping up the pressure solves some; the rest need an engineer. See F75.
Ignition faults (F.28 and F.29). F.28 means the boiler could not light at start-up; F.29 means it lost its flame and could not relight while running. Gas supply, a blocked condensate route and the flue all appear in Vaillant’s list of causes, alongside ignition parts. See F28.
Cold radiators. Sludge in older systems reduces circulation and can lead to the faults above. See cold radiators.
Servicing a Vaillant boiler
An annual service lets the engineer check the expansion vessel charge, the condensate trap, the electrodes and the combustion, which together cover many of the causes of the codes above. Vaillant guarantees generally depend on annual servicing, so keep the record. See boiler servicing.
When should you get an engineer?
If the pressure keeps falling, if an ignition code comes back after one reset, or if you see water inside the casing, the cause needs a Gas Safe registered engineer. The same applies to any code relating to the gas valve, the fan or the electronics. When you send an enquiry, include the full code shown on the display, the model name and how often you have needed to top up the pressure. The engineer will diagnose the fault and give a price before any work starts.