When your Vaillant boiler (ecoTEC and similar ranges) starts a heating cycle, the pump pushes water around the system. The boiler watches its water pressure sensor and expects to see a small, measurable change in pressure the instant the pump runs. The F75 fault code appears when the boiler starts the pump but sees no pressure change at all.
In plain terms, the boiler is asking: "I've turned the pump on — is the water actually moving?" If the answer comes back as "nothing changed," it shuts down and shows F75 to protect itself. It is essentially a safety lockout that stops the boiler firing when it can't confirm proper water circulation.
Some older online guides muddle this code up. To be clear: F75 is about no detected pressure change on pump start — it is not simply "low pressure." A separate low-pressure warning is a different matter (see the cross-link to F22 below).
Is it safe to keep using the boiler? No. Once it locks out on F75 it generally won't fire for heating or hot water until the underlying fault is sorted. Don't repeatedly reset it to force it back on — a genuine fault is being flagged for a reason, and dry-running a pump can cause more damage.
Because the fault is "pump ran, but pressure didn't move," it usually traces back to one of these:
Diagnosing which of these is at play needs test gear and access to internal components. That makes F75 largely an engineer job — but there's one thing worth checking first.
Before booking anyone, confirm your system pressure is correct. A genuinely low pressure can sit alongside or contribute to circulation problems, and it's the only homeowner-safe item on this list.
If pressure was fine, or topping up and resetting once doesn't clear the code, stop there. Everything beyond this — the pump, the pressure sensor, the expansion vessel, bleeding air from the pump head — sits inside the sealed system and should only be touched by a qualified engineer.
Why we stop here. Anything involving the pump, the expansion vessel, the sealed combustion side or removing the boiler casing is gas-appliance work. By law that's a job for a Gas Safe registered engineer (the body that replaced CORGI in 2009). If you ever smell gas, call the National Gas Emergency line on 0800 111 999.
The figures below are broad UK guide ranges for 2026 — actual prices vary by region, engineer and how accessible your boiler is. Treat them as indicative, not quotes.
| Job | Indicative cost (parts + labour) |
|---|---|
| Diagnostic call-out / fault-finding | £60 – £120 |
| Replace water pressure sensor | £100 – £200 |
| Re-pressurise / recharge expansion vessel | £90 – £180 |
| Replace expansion vessel | £150 – £300 |
| Replace circulation pump | £200 – £400 |
If a single repair runs into the hundreds, it's worth weighing against an annual cover plan — many policies bundle the boiler service, breakdown call-outs and parts into one monthly cost. Our guide on whether boiler cover is worth it walks through the maths, and you can compare boiler cover to see what's included.
These two codes look related but mean different things. F75 is "no pressure change detected when the pump starts." F22 is a low-water-pressure / dry-fire protection warning — usually a sign the system has lost water (often a leak or repeated venting). If your gauge reads near zero, you're more likely looking at an F22 situation. See our Vaillant F22 fault code guide for that one.
Book a Gas Safe registered engineer if:
If your boiler is already on a cover plan, this is exactly the kind of breakdown it's designed for — log the fault code with your provider so the engineer arrives prepared.
You can try a single front-panel reset after confirming the pressure is around 1–1.5 bar cold. If the code returns, the fault is genuine and needs an engineer — don't keep resetting it.
The code itself is a protective lockout, so the boiler shuts down safely rather than running with a circulation problem. It isn't a gas leak. But the underlying fault (pump or sensor) won't fix itself and needs a Gas Safe registered engineer. If you ever smell gas, call 0800 111 999.
Low pressure can contribute, which is why checking and topping up the gauge is the sensible first step. But F75 specifically flags "no pressure change on pump start," so a healthy gauge reading doesn't rule it out — often the pump or sensor is the real culprit.
Anywhere from a £60–£120 diagnostic if it's something minor like an air lock, up to £200–£400 if the circulation pump needs replacing. A pressure sensor sits in between. These are indicative 2026 UK ranges, not quotes.
Most boiler breakdown policies are designed to cover faults like this, including the call-out, diagnosis and parts — subject to the policy terms, exclusions and any age limits on the boiler. Always check what your chosen plan includes before you buy.
A breakdown plan can turn one-off F75 repair costs into a predictable monthly figure, with annual servicing included. Compare cover from our selected panel of providers.
Compare boiler coverInformation, not advice. Boiler Cover UK is an independent comparison site featuring a selected panel of providers, not the whole market, and we may earn a commission. Gas work must always be carried out by a Gas Safe registered engineer.