What changes the cost of fitting a Durgo valve?

What is a Durgo valve?

A Durgo valve is an air admittance valve, often called an AAV. Durgo is a manufacturer's name, but people use it for any valve of this type in the same way they say Hoover for a vacuum cleaner. The valve sits on top of a soil stack or on a waste pipe inside the house, usually hidden in a loft, a boxed-in corner of a bathroom or the cupboard under a sink.

When you flush a toilet or empty a bath, the falling water pulls air behind it. If no air can get in, it can pull the water out of the traps under sinks, basins and baths. Those traps are what stop drain smells coming into the room. An air admittance valve opens to let air in when that happens and closes again straight after, so smells stay in the pipe.

QuoteZila is starting in Cheshire, with Crewe, Nantwich and Sandbach among the first towns, and anyone in the UK can post a job. We have not put a price on this page. We found no dated public source for what fitting or replacing one of these valves costs, so this guide covers what changes a plumber's quote and what each quote should say.

Signs that a valve may need attention

Air admittance valves have a moving seal inside. Over years it can stick open, stick shut or get clogged with dust. These are the things people tend to report:

• A sewer smell in a bathroom, loft or cupboard, strongest near the valve.
• Gurgling from a sink, basin or bath when the toilet is flushed or another fitting drains.
• Traps losing water, so you can see less water in the toilet bowl or smell drains from a plughole.
• Slow draining across several fittings at once.
• A whistle or rattle from the boxed-in pipe when water drains.

None of these prove the valve has failed. A partial blockage in the soil stack or underground drain can cause the same symptoms, and fitting a new valve will not fix it. That is why a good plumber will want to look before they price.

Types of air admittance valve

There are two broad kinds, and the quote should say which one is involved:

• Stack valves. A larger valve on top of the main soil stack, often in the loft or at the top of a boxed-in pipe in the bathroom. These protect the whole system above and below.
• Branch or mini valves. Smaller valves fitted on a single waste pipe, for example under a kitchen sink, on a basin waste or on a washing machine standpipe, where the pipe run is long or awkward.

Within each kind there are different sizes and makers, and some valves are made for lofts or unheated spaces where cold could affect the seal. Ask the plumber to name the valve, its size and where it will go. If yours is a Durgo, the plumber may replace it with the same brand or an equivalent valve from another maker.

What changes the price of the job

If one quote is much lower than another, look first at whether it includes finding the cause, opening and making good the boxing, and VAT. Those lines explain most gaps in a small job like this.

Before you call a plumber

A few minutes of preparation helps a plumber price accurately:

1. Note when it happens. Does the smell or gurgling come after the toilet flushes, when the bath drains, or all the time?
2. Find the valve if you can. It may be in the loft at the top of the soil pipe, or behind a panel in the bathroom. Take a photo if you can see it without removing anything.
3. Check the traps. Look at whether the water level in the toilet bowl drops, and whether the smell is strongest at one plughole.
4. Note the outside pipes. Is there a soil pipe running up the outside wall, and does it have an open top above the roof line?
5. Mention any recent work. A new bathroom, extension or kitchen can change how the drainage is vented.

Give every plumber the same description and the same photos. That makes the quotes easier to compare.

When a new valve is not the answer

Sometimes the plumber will tell you the valve is fine. Other causes include:

• A partial blockage in the soil stack or underground drain, which may need clearing by a drainage company.
• A trap that is too shallow or the wrong type for the fitting.
• Long or badly sloped waste pipes that siphon traps however well they are vented.
• An outside vent that is blocked by leaves, a bird's nest or a cap that should not be there.
• A cracked joint or pipe that lets smells escape.

Where an air admittance valve can be used is covered by the building regulations guidance on drainage, and most systems still need an open vent to the outside somewhere. If the plumber says a valve is not suitable in your spot, ask them to explain the alternative.

If the work turns into a larger change to the bathroom or drainage, GOV.UK says installing a bathroom that involves plumbing may need building regulations approval, and that you do not need to arrange it yourself if the installer is registered with a competent person scheme ^[S4].

How to compare quotes

Citizens Advice says a quote is a fixed price, while an estimate is only a guess at the cost ^[S1]. It suggests getting written quotes from at least three traders, and says some traders charge for giving a quote, so ask first ^[S1]. For a valve job, ask each quote to state:

1. What the plumber thinks is causing the problem, and how they checked.
2. The valve to be fitted, its size and maker.
3. Whether opening and refitting boxing or panels is included.
4. Who makes good tiles or paint, and whether that is in the price.
5. Whether an access panel is included or offered.
6. Any minimum or call-out charge.
7. Whether the price includes VAT. A business must register for VAT when its taxable turnover goes over £90,000 ^[S2].

WaterSafe keeps a register of approved plumbers you can search ^[S3]. Whoever you choose, agree in writing what happens if they open the boxing and find a bigger problem.

Jobs you might post

These are examples, not taken from real job posts.

• "Smell of drains in the upstairs bathroom, worst near the boxed-in soil pipe. Think the valve at the top may have failed."
• "Kitchen sink gurgles every time the washing machine empties. Would like it looked at and fixed."
• "Air admittance valve in the loft is cracked. Please replace like for like and check the stack."

Say where the valve is, what you can smell or hear and when, and anything that affects access, such as a tiled box or a loft without boards.

Get quotes from plumbers

Describe the problem and your postcode. Up to five matched local businesses can send you a quote ^[QZ2]. QuoteZila is free for customers and local businesses ^[QZ1].

Posting a job is not open yet

See our plumbers and bathroom fitters pages, and the plumber cost guide for how plumbing prices are built. If the whole bathroom is changing, see what changes the cost of a new bathroom.

Questions about Durgo valve prices

Part of Cost guides. All services

Related trades

• Plumbers
• Bathroom fitters

Cost guides

• Plumber cost

Related pages

• Kitchen Sink Replacement Cost: What Changes the Price. What changes the cost of a kitchen sink replacement in Cheshire: inset or undermount, the worktop cut-out, the waste, the tap and appliance connections.
• New Toilet Cost: What Changes the Price to Fit One. What changes the cost of a new toilet in Cheshire: the style, the cistern, moving the soil pipe, the floor and removal of the old one, and what to ask.

Sources

1. QZ1: QuoteZila product fact. QuoteZila home and jobs-for-tradesmen copy.
2. QZ2: QuoteZila product fact. QuoteZila FAQ and app README.
3. S1: Before you get work done on your home, Citizens Advice. Accessed 2026-10-25. https://www.citizensadvice.org.uk/consumer/getting-home-improvements-done/before-you-get-building-work-done/
4. S2: Register for VAT, GOV.UK. Accessed 2026-10-25. https://www.gov.uk/register-for-vat
5. S3: WaterSafe Register home page, WaterSafe. Accessed 2026-10-25. https://www.watersafe.org.uk/
6. S4: Building regulations approval, GOV.UK. Accessed 2026-10-25. https://www.gov.uk/building-regulations-approval