Vaillant F.74 fault codewhat it means and how to fix it
The water pressure sensor is sending a signal that is too high to be genuine. This is a wiring or sensor fault, not high system pressure.
Take care
Get a Gas Safe registered engineer to look at your Vaillant F.74
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What is the pressure gauge showing?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
A perfectly normal 1.0 to 1.5 bar
Exactly what you would expect. The gauge is mechanical and independent of the sensor, and its agreement with reality confirms the fault is electrical.
Do not add or release water. Book an engineer to test the sensor and its wiring.
It really is sitting near or above 3 bar
Unusual with this code, but it changes matters. A filling loop left open or a failed expansion vessel can genuinely over-pressurise a system.
Check the filling loop is fully closed and mention the reading when you book. Do not attempt to release pressure yourself.
There is damp or staining around the boiler
Water in the connector is a leading cause, and the sensor may test perfectly well once the connector is dried and the leak stopped.
Point out the damp so the leak is dealt with rather than the sensor simply being replaced.
What F.74 means
F.74 means the signal arriving from the water pressure sensor sits above the range the boiler will accept as valid. It is worth being clear about what that does and does not mean, because the wording misleads people constantly: F.74 is not the boiler telling you the heating system is over-pressurised. It is the boiler telling you the electrical signal from the sensor is implausible. A pressure sensor returns a voltage that varies with pressure, and the board knows what the highest credible voltage looks like. Anything above it cannot represent real system pressure, so the reading is rejected and the appliance stops.
In practice that points at a short circuit to a supply line, water inside the connector, or a failed sensor. Checking your pressure gauge is still worth doing, but expect it to read perfectly normally. Two ranges use the number differently, and the page would be wrong for them if it did not say so.
On the ecoTEC sustain, F.74 is the water pressure sensor "not connected" — an interruption in the sensor or its supply line — because that manual gives the short circuit to F.73. On the ecoTEC plus CS/1-5 sold since 2022, F.074 is likewise "the signal for the water pressure sensor has been interrupted", and there is no F.073 to pair with it. On the ecoTEC plus, pro, exclusive, ecoFIT and the 2005 to 2012 ecoTEC the high-side reading described above is what Vaillant print. In every case the boiler has rejected the sensor signal rather than measured high pressure.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Short circuit in the sensor wiring | A chafed conductor touching a supply line pulls the signal line high and produces an impossible reading. | Common |
| Moisture in the sensor connector | Water across the pins bridges the signal to an adjacent contact, which the board reads as excessive voltage. | Common |
| Failed pressure sensor | The sensing element can fail in a way that leaves its output stuck at the top of its range regardless of pressure. | Common |
| Board input damage | Considered last, and only once the sensor has been substituted and the wiring proven sound end to end. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£90–£250
Pressure sensor £120 to £200 fitted. Connector or wiring repair often within a call-out of £80 to £150.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Vaillant ecoTEC water pressure sensor
0020059717£26–£54Authorised Vaillant parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Vaillant fault codes
- F.22Get it checkedThe boiler has shut down because there is not enough water in the system. Pressure has dropped below roughly 0.5 bar and it will not fire until you top it up.Related: water pressure
- F.75Get it checkedThe boiler cannot detect a rise in pressure when the pump starts, so it has locked out. Usually a failed pressure sensor or a pump that is not moving water.Related: water pressure
- S.53Get it checkedNot a fault. Your boiler is in a deliberate waiting period because the gap between flow and return temperatures is too wide, which points at poor circulation.Related: water pressure
- F.73Get it checkedThe pressure sensor signal is out of range at the low end. Usually the sensor or its wiring, rather than the pressure itself.Related: water pressure
- S.76Get it checkedA service message, not a lockout: the heating water pressure has dropped and Vaillant want it topped up. The boiler is still running, but below 0.5 bar it will stop with F.22.Related: water pressure
- S.41Get it checkedA status, not a lockout: the heating water pressure is too high, above about 2.8 bar. Usually an over-filled system or a tired expansion vessel, and the safety valve will discharge above 3 bar.Related: water pressure
Own a Vaillant boiler? Save it and its codes come first next time.
Related guides
Common questions about Vaillant F.74
Is F.74 the opposite of F.73?
On the ecoTEC plus, pro, exclusive and ecoFIT, yes: F.73 is the pressure sensor signal falling below the valid range and F.74 is it rising above. On the ecoTEC sustain the pair is printed the other way round, F.73 for a short circuit and F.74 for a break. Neither is a statement about your actual system pressure — both say the signal itself cannot be trusted.
Should I drain some water out to reduce the pressure?
No. In the great majority of F.74 cases the pressure is entirely normal and draining would leave you with a genuine low pressure fault on top of the existing one. Read the gauge, write down what it says, and leave the water alone.
Why does it sometimes clear on its own?
Because moisture dries and a marginal connection can remake itself as the boiler warms. Intermittent behaviour is a strong hint that the fault is in the wiring or the connector rather than the sensor.
What does putting it right cost?
A pressure sensor is £120 to £200 fitted. A wiring or connector repair frequently falls inside a call-out charge. It is one of the cheaper Vaillant faults provided the diagnosis is done in the right order.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.