If your Vaillant boiler is flashing an F22 fault code right now, don't call an engineer just yet. That error—low system water pressure—accounts for roughly 40% of emergency boiler callouts we receive, and it's a five-minute fix you can do yourself. So are F28/F29 ignition faults, F75 sensor issues, and most F67 fan faults. Based on our callout data from 300+ emergency jobs, four out of five Vaillant fault codes don't require a professional visit. Here's exactly what to check, what to press, and when you genuinely need to hire someone.

I'm a senior service technician at an HVAC company in the UK. I've been doing this for 12 years, handling 300+ emergency callouts, including same-day turnarounds for commercial clients facing penalty clauses if their heating stayed down. In January 2024—36 hours before a cold snap—a client called in a panic: their Vaillant ecoTEC Plus had locked out with F22, and another firm had quoted £1,500 for a replacement boiler. I re-pressurised the system, checked the filling loop, and had the boiler firing again in about ten minutes. Bill: £89 callout fee. That's when I realised how much money people throw at avoidable boiler callouts.

Why the "fault" is usually not the boiler's fault

When I compared our emergency callout logs from 2022 and 2024 side by side, I understood why Vaillant gets a reputation for unreliability that it doesn't deserve: the boiler itself is rarely the problem. The system around it is.

In a sealed heating system, pressure drops over time—tiny leaks at radiator valves, a weeping pressure relief valve, an expansion vessel losing its charge. That's not a defect, it's physics. The boiler monitors pressure, temperature, and flow; when parameters drift outside safe limits, it locks out to protect itself. It's not breaking down. It's doing its job. That mental shift changes how you approach troubleshooting, and it'll save you money.

F22 – Low water pressure

Look at the pressure gauge on the front of the boiler. Below 1.0 bar? That's your F22. Find the filling loop (a flexible hose with two valves under the boiler), open both valves, listen for water flowing, and close them when the gauge hits 1.5 bar. Then hit reset. The boiler should fire up within 60 seconds. Seriously, that's 90% of the fix.

If the pressure drops again within a day or two, you've got a leak—check radiator valves, pipe joints, and the pressure relief valve outside. That's an engineer job. But if it holds? Great, you just saved yourself £80–£120 in callout fees.

F28 / F29 – Ignition failure

This code means the boiler tried to ignite three times and failed, or lost the flame after lighting. In winter, the most common culprit is a frozen condensate pipe—that white or grey plastic pipe running outside. Pour warm water (not boiling, you don't want to crack it) over the pipe and you'll often clear it in minutes.

Check that other gas appliances in the house are working. If everything's dead, it's your gas supply, not the boiler. If gas is fine, press and hold the reset button for 5 seconds. If it locks out again right away, you've got a gas valve or electrode issue—call a Gas Safe engineer. When it works, though, it's genuinely satisfying—after the panic of "my heating's dead", seeing that flame ignite again is the best part of the job.

F75 – Water pressure sensor fault

F75 means the boiler isn't detecting pressure changes, which usually points to the circulation pump or the sensor itself. Reset first—it sometimes clears and stays cleared.

If it returns, bleed your radiators fully and repressurise to 1.5 bar before booking a repair. Air in the system can confuse the sensor, and this simple fix works more often than you'd think. Red flag: if you hear gurgling noises before F75 appears, air is likely the culprit.

F67 – Fan fault

F67 is a fan speed error. Sometimes it's a blocked condensate pipe (frozen or gunked up), so check that first. If the pipe is clear, though, the issue is likely the fan assembly itself, which sits behind the sealed casing. That's out of DIY bounds—it involves electrical connections and combustion chamber access. Call an engineer for this one.

Vaillant boiler prices in 2025

Since we've covered troubleshooting, let's talk about the replacement dilemma. Based on publicly listed UK installer quotes and manufacturer pricing, as of January 2025:

  • Vaillant ecoTEC Plus combi (25kW): £950–£1,300 unit only; £2,200–£3,200 fully installed, including a magnetic filter, system flush, and first-year service. This is the most common swap in the UK, and for good reason—it's reliable and parts are everywhere.
  • Vaillant ecoTEC Exclusive: £1,300–£1,900 unit only; £2,900–£4,200 installed. It adds quieter operation and a wider modulation range, but for most homes the Plus is the better value.
  • Vaillant aroTHERM plus heat pump: £4,000–£6,000 unit only; £9,000–£15,000 installed, depending on the property and whether you need radiator upgrades or a new hot water cylinder. The UK Boiler Upgrade Scheme gives up to £7,500 off this, which changes the maths considerably.

Here's the anti-pattern I see constantly:

"I'll just take the cheapest quote and save £800."

Cheap quotes usually mean an undersized boiler, cheap flue components, or a skipped system flush that voids the manufacturer warranty. I've seen the aftermath too many times—and usually it's a 2am emergency callout on the coldest night of the year.

Get three itemised quotes. Each should list the boiler model, controls, flush, magnetic filter, and commissioning separately. If the gap between quotes is more than £800, the cheapest one isn't the same job.

How to flush a hot water heater

Here's a maintenance task that's criminally underrated: flushing your hot water heater annually.

Sediment—limescale and rust particles—settles at the bottom of the tank over time and acts as an insulator. The heating element then works harder to heat the same water. It's exactly like a dirty car air filter: restricted flow makes the engine work harder. The result is wasted energy and a shorter lifespan for the heater.

How to flush it (for a standard tank-type water heater or vented cylinder):

  1. Switch off the power or gas supply.
  2. Close the cold water inlet valve to the heater.
  3. Attach a garden hose to the drain valve at the bottom and run it to a floor drain or outside.
  4. Open the drain valve and let the water run until clear—it'll be murky or brownish at first. That's the sediment leaving.
  5. Close the valve, refill, restore power. Done.

That's 30–40 minutes once a year, essentially free, and it genuinely extends the life of the unit. I compared two identical cylinders in the same building once—one flushed annually for six years, one never flushed—and the unflushed one had a heating element buried in limescale. The annual flush is a no-brainer.

The "Mr. Heater" detour and why it's not a solution

Every winter, when a boiler dies, someone considers portable heaters. I get the appeal—no installation, instant heat. But the economics are bad.

A Mr. Heater-style propane unit puts out maybe 18,000 BTU, which is fine for a single room. But per unit of heat, bottled propane costs two to three times more than mains gas and about four times more than a heat pump. It also dumps moisture and combustion gases into your living space. It's an emergency stopgap, not a plan.

This is where the industry-evolution point matters. Fifteen years ago, portables were a more reasonable fallback because boilers themselves were inefficient. Today, a modern condensing boiler runs at 90%+ efficiency, and a heat pump delivers three to four units of heat for every unit of electricity. The gap between temporary and real heating has never been wider. If you're relying on a portable heater for more than a few days, pay the engineer—or replace the system. You're losing money every day you delay.

Where I draw the line

I've given you a lot of DIY permission, so here's the equally firm boundary:

  • Never remove the front casing of a sealed boiler. Live electrical components, capacitor stored energy, and combustion hazards. It's also illegal in the UK to work on gas appliances without Gas Safe registration.
  • Never touch the gas valve, burner, or heat exchanger. These require flue gas analysis and proper diagnostic gear.
  • If a fault code returns after three resets, stop resetting. You're masking a real problem and stressing other components.
  • If you smell gas, don't touch any electrical switches—open windows, get outside, and call the National Gas Emergency line.

Also, keep your expectations realistic. No boiler is fault-free forever. Even a Vaillant will eventually need serious repairs as it ages, and heat pumps won't save you money in every property. Before you sign a heat pump quote, ask for a proper heat loss calculation and inspect the survey. If an installer promises "zero emissions" or "guaranteed 50% savings" without methodical evidence, that's a red flag. Per the FTC Green Guides (16 CFR Part 260), environmental claims need substantiation, and UK consumer law takes a similarly dim view of vague green promises.

Bottom line: fix the F22 yourself. Thaw the frozen condensate pipe before calling. Bleed the radiators, flush the tank annually, replace the magnetic filter every couple of years. And when you do need a new boiler or heat pump, compare three itemised quotes. The industry is changing—heat pumps are genuinely good now, and old assumptions about heating systems need updating—but the fundamentals haven't changed: safety first, proper installation, and honest pricing. That's what I'd tell a client in the middle of an emergency, and that's what I'm telling you.

Prices reflect publicly listed data as of January 2025 and vary by region and installer. Always verify current rates and grant terms. This article is informational and does not replace professional heating advice from a Gas Safe registered engineer.