Vaillant F22 fault code: low water pressure, and when it clears

What F22 means: a safety switch-off for low water pressure

F22 is a protective shutdown rather than a broken part. The boiler measures the water pressure in its sealed heating circuit, and when there is too little to run safely it stops and shows the code. On a combi that means no heating and no hot water until the pressure is back up.

The fault table in Vaillant's ecoTEC plus operating instructions (0020308119_03, appendix C) lists F.022 as "No/insufficient water in the product or the water pressure is too low." It is one of only two codes in that homeowner table, and the measure Vaillant gives is to check the filling pressure and top up with heating water.

If you have never used the filling loop, the same manual's advice is: "Have your competent person explain the filling and purging process to you."

Your pressure reading, and what to do

Read the pressure with the heating off and the radiators cool, then find your row below. Each reading names the Vaillant document it comes from, and the two manuals cover different model ranges. The 0.5, 0.8 and 1.1 bar points apply to ecoTEC plus ..6/5-5 models (installation manual 0020244997_02, section 7.9). The operating manual quoted below (0020308119_03) covers ecoTEC plus ..CS/1-5 models. Other Vaillant models may switch off at different points.

Check the model name on your boiler's data plate first, and follow the manual for that model where it differs from this page.

Check and top up, in this order

Everything here happens outside the boiler. Vaillant's page on pressure loss is plain about it: "Do not remove the boiler casing yourself."

1. Read the pressure. On ecoTEC plus ..CS/1-5 models (operating manual 0020308119_03), the display also shows it under the INFORMATION menu as Water pressure.

2. If the reading is 1 bar or more, add no water. Vaillant UK's fault code page splits its advice at 1 bar: below it, a top-up "can be solved without an engineer if you are competent to do so", and above it F22 is "a case for a Vaillant engineer". The page is silent on exactly 1 bar, which already sits inside its normal range, so treat 1 bar as engineer territory too.

3. Only if the reading is below 1 bar, top up slowly through the filling loop to between 1.1 and 1.5 bar. 1.5 bar is the top of the range on Vaillant UK's fault code page, and on ecoTEC plus ..6/5-5 models the figure keeps flashing until it reaches 1.1 bar (installation manual 0020244997_02, section 7.9). Filling loops differ between Vaillant models: our Vaillant boiler pressure page and the guide to increasing boiler pressure show the loop itself.

4. Close the filling loop fully once you reach the target, following section 5.4.2 of operating manual 0020308119_03 for your model.

5. Give the boiler the chance to restart on its own. On ecoTEC plus ..CS/1-5 models, operating manual 0020308119_03 says F.22 clears without a reset once the pressure is back up (see the next section).

6. If the pressure is back in range and F.22 is still on the display, reset once only. On ecoTEC plus ..CS/1-5 models, operating manual 0020308119_03 (section 3.1) says to press and hold the reset button for more than three seconds. On other models, follow your own manual.

7. If it still will not clear, stop and book a Gas Safe registered engineer. If it does clear, read the gauge again the next day: a fall since the top-up means water is escaping somewhere.

Does F22 clear by itself after a top-up?

On ecoTEC plus ..CS/1-5 models, yes. Their operating manual (0020308119_03, section 5.4.2) says: "Fault message F.22 goes out and the product automatically works again once a certain pressure level is reached again."

ecoTEC plus ..6/5-5 models are covered by a different document, installation manual 0020244997_02. Section 7.9 of that manual says the pressure figure keeps flashing until it reaches 1.1 bar, so on those models a flashing display partway through a top-up is normal and not a reason to press reset.

That is the useful difference from most fault codes. With F22 the fix is the water, not the reset button, so a reset is only the fallback when the code stays on after the pressure is back in range.

What pressure suits your home

Vaillant's documents give slightly different figures, so it helps to know which one says what. Vaillant UK's fault code page gives 1 to 1.5 bar as the normal range. The ecoTEC plus ..CS/1-5 operating manual (0020308119_03, section 5.4.2) recommends at least 1.0 bar, a good standard value of 1.5 bar and a maximum of 2.5 bar. The ecoTEC plus ..6/5-5 installation manual (0020244997_02, section 7.9) gives 1.0 to 2.0 bar with the system cold, and Vaillant UK's page on losing pressure gives an operating range of 0.7 to 2.5 bar.

Add height for taller homes

Operating manual 0020308119_03 says to add 0.1 bar to the minimum for each metre of height up to the highest radiator. Its worked example, a system 8 metres from cellar to roof, gives a target of 1.8 bar.

That matters in town houses, loft conversions and flats over several floors. The installation manual (0020244997_02) makes the same point in its own words: installations over several storeys may need a higher filling pressure to stop air getting in.

Even so, do not work out a higher figure and fill past 1.5 bar on your own, the top of the range on Vaillant UK's fault code page. Ask the engineer who services your boiler to confirm the cold pressure that suits your home, and write it down next to the boiler.

F22 keeps coming back: stop topping up

One top-up after bleeding radiators is expected. Vaillant's page on pressure loss names "Releasing air or water from a radiator when bleeding it" as a cause, and the operating manual says the pressure level falls after purging, so check the gauge again afterwards.

Repeated top-ups are a different matter. If the pressure drops again after a top-up and nobody has bled a radiator, stop topping up and book a Gas Safe registered engineer. A sealed system should hold its water, and Vaillant names "A leak from the appliance or on the system most commonly from radiator valves or system components" as the usual reason it does not.

Topping up again and again only hides the cause. Each top-up replaces water that has escaped somewhere, and the leak keeps going until someone finds it.

Before the visit, look without touching anything: check under the boiler, along any pipes you can see and around each radiator valve for drips, damp patches or staining. Note how often you have topped up and the reading each time. Leave pipe joints alone: Vaillant's advice is "Do not attempt to repair loose or broken pipework joints unless you are trained to do so."

If there is no visible leak, the engineer will look at the parts that keep the pressure steady, such as the pressure relief valve and the boiler's internal expansion vessel. Vaillant UK's fault code page lists "Internal expansion vessel faulty" as an F22 cause.

F22 with the pressure already in range

If the gauge reads normally and F.22 will not clear after one reset, the cause is likely inside the casing. An engineer will check the plug and cable to the heating pump or water pressure sensor, the sensor itself and the pump, then run check programme P.0 (installation manual 0020244997_02). These are the F22 causes listed on Vaillant UK's fault code page, all engineer work:

• "A problem with the water pressure sensor" or "Water pressure sensor faulty": the boiler may be misreading a system that is actually full.
• "Loose, disconnected, or faulty wiring for the pump or pressure sensor".
• "Internal expansion vessel faulty".
• "The pump may not be working properly (Open vented boilers only)."

Staying safe with F22: what not to touch

F22 is a water fault, not a gas fault, and the boiler has already made itself safe by switching off. Keep the casing on: Vaillant UK's fault code page advises, "We strongly advise that you do not gain access inside your boiler as this can be dangerous."

Do not drain water from the system, open the pressure relief valve or loosen fittings to change the pressure, and reset once at most.

If you ever smell gas, call the National Gas Emergency Service on 0800 111 999 straight away, and do not reset or relight anything.

What Smart Plan does and does not pay for with F22

When F22 is caused by low pressure, the fix is a top-up, and the plan does not pay an engineer to do one. Repressurising equipment and resetting equipment are both general exclusions in the terms (10.2 and 10.1). If an engineer attends and the only job is a top-up or a reset, a £95 call-out fee may apply, only in the situations set out in the terms (clause 9.2).

Smart Plan is a service plan, not insurance, from UK Boiler Company Ltd. It is for breakdowns after you join, so an F22 already on the display, or a leak that was already there, counts as a defect once it is identified, and repairing defects is excluded (Definition 14 and general exclusion 10.13).

Where F22 comes from a failed part, such as the water pressure sensor, a repair would fall under the boiler cover limit in clause 2.1(d): £500 for a boiler under 7 years old, or £200 for a boiler over 7 years old, including parts and labour (2.1(d)), for each 12-month period from the start of your agreement (Definition 12). Every repair is still subject to the exclusions in the terms. The terms exclude works caused by sludge, scale, corrosion or increased pressure (10.22), so a part damaged by an overfilled system may not be covered.

Where a leak found during a breakdown call-out is repaired, the terms say the repair uses compression or push-fit fittings as short-term leak prevention (2.1(f)), and it is still subject to the exclusions. Central heating parts such as system pipework are only within the plan on Boiler & Central Heating Cover (section 2). Tracing and getting access to a hidden leak is excluded (10.24), and so are works on pipework within the fabric of the building (10.5). Replacing or repairing radiators is excluded (2.2(e)), so a radiator that is itself leaking falls outside the plan.

A failed PCB or heat exchanger means the boiler is treated as beyond economic repair under clause 2.1(c), and a contribution under clause 9.5 applies instead of a repair.

Engineers attend Monday to Friday, 08:00 to 18:00, unless it's an emergency breakdown. For what Vaillant's own repair options involve next to a cover plan, see Vaillant boiler cover and repair costs.

Set up cover before the next breakdown

A top-up is something you do yourself, not something a cover plan pays for. Smart Plan is for the next breakdown, such as a part that fails after you join. Leave your number for a free call back. It's a service plan, not insurance.

Helpful links

• All Vaillant fault codes
• Vaillant boiler pressure
• How to increase boiler pressure
• Boiler losing pressure
• Vaillant F75 pump and pressure fault
• Vaillant boiler cover and repair costs
• Vaillant's official boiler fault codes
• Vaillant: why is my boiler losing pressure?
• Vaillant ecoTEC plus operating instructions (0020308119_03, PDF)
• Check an engineer on the Gas Safe Register