Vaillant [S.41] status codewhat it means

S.41 is the status "Water pressure too high — the system pressure is too high", and the ecoTEC exclusive manual gives the figure: "water pressure > 2.8 bar". The boiler is not locked out. It is telling you that the sealed heating system is carrying more pressure than it should, and that the next stop is the pressure relief valve, which opens at 3 bar and dumps water through the copper pipe that ends outside.

Vaillant's operating instructions for the ecoTEC sustain put the householder response in one line: "the system pressure is too high: > 0.3 MPa (> 3 bar) — wait until the excess heating water has flowed out through the expansion relief valve", which is honest about what will happen but not something to rely on twice, because a relief valve that has lifted often fails to reseal and then weeps for good. The two common causes are simple. The system was filled too far, to 2 bar or more when cold, so that ordinary expansion as it heats pushes it towards 3 bar; or the expansion vessel has lost the air charge that lets it absorb that expansion, so the pressure swings between low when cold and very high when hot.

A combi has a third route: a pinhole in the plate heat exchanger or a passing filling loop lets mains water at 3 or 4 bar creep into the heating side, and the pressure climbs over days with nothing switched on. F.74 is the fault version, raised when the pressure sensor's signal is too strong, and its remedy in the installer table is "drain water, check the water pressure sensor". The 2022 ecoTEC plus shows S.041.

1. 1

   Check both valves on the filling loop are fully closed, and if your loop is the flexible detachable kind, that it is disconnected. Then read the pressure with the boiler cold. Vaillant's range is 1.0 to 2.0 bar cold; the top of the bar graph on the display marks 2.0.

2. 2

   If it is above 2.0 bar cold and you filled it recently, let a little water out at a radiator bleed valve into a cloth or cup until the display reads about 1.2 to 1.5 bar. Do it slowly and stop early; it is easier to add than to remove.

   Do not open the boiler's pressure relief valve to lower the pressure. It rarely reseals properly once lifted by hand and will drip outside for good.
3. 3

   Watch the pressure over the next few heating cycles. If it climbs above 2.5 bar every time the boiler is hot and falls back when cold, the expansion vessel needs recharging or replacing. If it climbs with the boiler off and the loop closed, water is getting in from the mains, and both are engineer's work.