CO2 Pressure Systems for Pubs in 2026

Last updated: 2 May 2026

Most pub licensees don’t check their CO2 pressure system until something breaks, and by then you’ve lost a full keg, wasted product, and disappointed customers waiting for a pint. The pressure regulator in your cellar is not a “set and forget” piece of kit — it’s a safety device and a profit protector that demands regular attention. If you’re taking on a pub or troubleshooting cellar issues, understanding how your CO2 system works, what pressures should be running, and when to call an engineer could save you hundreds of pounds and your reputation.

This article walks you through CO2 pressure systems in UK pub cellars: how they work, what pressures are correct, maintenance schedules, common failures, and the cost reality. I’ve been through NSF audits, EHO inspections, and cellar emergencies on the Marston’s CRP agreement — and pressure issues come up every time.

How CO2 Pressure Systems Work in Pub Cellars

A CO2 system in your cellar does one job: it pushes liquid out of a keg through the pipework and into a glass. Understanding the components and pressures involved stops you from running blind when something goes wrong.

Your typical pub cellar setup includes: a CO2 cylinder (usually shared or in a battery), a regulator (which sits on top of the cylinder), a pressure gauge (which shows you the pressure), a main isolating valve, secondary regulators on individual lines, and then the lines themselves running to your taps upstairs. The regulator’s job is to take the very high pressure inside the cylinder (around 50–60 bar) and reduce it to a usable serving pressure — usually 2.5 to 4.0 bar depending on the beer style and line length.

The most common misunderstanding is that the pressure gauge shows you everything. It doesn’t. The gauge on the regulator shows you the outlet pressure — the pressure being pushed toward the kegs and lines. If that gauge reads 3.5 bar, that’s what’s being delivered. But if a regulator has drifted or a secondary line regulator has failed, you might be pushing 5 bar into a line set for 2.5 bar, which over-carbonates the beer and creates foam issues upstairs.

The system is pressurised at every point. A leak anywhere — a loose fitting, a cracked seal on a keg coupler, a pinhole in a line — means pressure loss and product loss. That’s why beer line cleaning and cellar inspection are part of the same job: you’re looking at fittings, connections, and line integrity.

Correct CO2 Pressure Settings for Draught Beers

Pressure varies by beer type, and running the wrong pressure ruins the product before it reaches the customer. Here’s the practical breakdown:

• Ales (cask or keg): 1.5 to 2.5 bar. These beers are less carbonated and over-pressurising them creates excessive foam and destroys the flavour profile.
• Lagers and mainstream keg beers: 2.5 to 3.5 bar. This is the standard range for most UK pubs. Most Marston’s lines run at 3.0 bar.
• Craft kegs and IPAs: 2.5 to 3.0 bar. Check your supplier’s spec — craft breweries often print the correct pressure on the keg label.
• Stouts and nitro pours: These run on mixed gas (nitrogen and CO2) and require specialist regulators. Standard CO2 pressure will make them foam immediately.

The pressure you set should be slightly above the natural carbonation level of the beer, but not so high that you’re forcing over-carbonation. A rule of thumb: you need 0.5 to 1.0 bar of excess pressure to push liquid from the keg through the line to the tap reliably. If your line is 15 metres long (as mine is from cellar to ground floor at Teal Farm), you’re fighting friction and may need to run slightly higher than a 3-metre line.

The easiest way to get this right is to check your BDM’s cellar spec sheet or your original keg supplier documentation. Marston’s CRP pubs get a cellar map with every tie — it tells you the pressure for every line. If you’ve inherited a pub without documentation, photograph the setup and ask your BDM for a formal spec. It’s their responsibility to provide it.

Daily, Weekly and Monthly Pressure Checks

Pressure checks are a legal compliance requirement under food safety law, not optional housekeeping. Your EHO inspector expects to see a documented log of checks. When I passed my 5-star EHO rating at Teal Farm, cellar temperature and pressure logs were part of the audit trail.

Daily Checks (Opening Routine)

Every morning when you open the cellar, look at your main regulator gauge. It should read what you expect. If you run 3.0 bar, the gauge should show 3.0 bar. If it shows 2.5 or 3.5, something has shifted. Record this on a simple log. If the gauge fluctuates by more than 0.2 bar from one day to the next, call an engineer — the regulator may be failing.

While you’re down there, do a quick visual check: any puddles under kegs or connections? Any obvious cracks in regulator seals? Any hissing sounds? These are signs of a leak. A leak that costs you 0.5 bar per day costs you a full keg of product every three weeks.

Weekly Pressure Tests

Once a week, check each line individually. Your regulator might show 3.0 bar at the main, but if a secondary regulator has failed or a connection has loosened, an individual line might be running at 2.0 bar or 4.5 bar. You can do this with a simple pressure test kit (around £40–60) that clips onto a keg coupler momentarily. Record the reading for each line.

If a line is more than 0.3 bar off spec, investigate: tighten fittings, check the secondary regulator, or call your engineer. Don’t ignore it because “the pints taste okay today” — a pressure drift will get worse and eventually you’ll be serving flat beer or excessive foam.

Monthly Deep Audit

Once a month, do a full system check: regulator condition (seals, casing, connections), gauge accuracy, cylinder status, all line pressures, and any visible wear. Document it. This log becomes your defence if the EHO challenges you on cellar maintenance or if a supplier claims you’ve damaged a keg.

Before you take on any tied pub, ask to see the previous licensee’s pressure logs. If they don’t exist, that’s a red flag — the cellar hasn’t been properly managed. If they exist and show consistent variance, the equipment needs replacing before you sign.

Common CO2 Pressure Problems and Solutions

Here are the failures I’ve encountered and the reality of fixing them:

Gauge Reading Drifts Upward

The regulator is sticking or the internal spring has weakened. A stuck regulator will creep higher over days, over-pressurising everything. Stop using it immediately. Call an engineer. A replacement regulator costs £150–300 fitted. A new gauge alone (if the regulator itself is fine) is £40–80.

Gauge Reads Zero But You Still Have Pressure

The gauge itself has failed internally or the connection has cracked. The line is still pushing pressure but you can’t see it. This is dangerous because you think you’re at 3.0 bar but you’re actually at 4.5 bar. Answer: replace the gauge immediately. Don’t wait. This costs £40–80 and takes 20 minutes.

Pressure Drops Steadily Over Hours or Days

You have a leak. Start at the cylinder and work forward: check the main isolating valve, the regulator connection (tighten it by hand first), all keg couplers, and then the lines themselves. If tightening connections doesn’t fix it, you likely have a slow leak in the regulator seal or a tiny crack in a line. An engineer can pressurised-water test the system to find it. Cost: £60–120 for a call-out plus repair.

One Line Loses Pressure While Others Hold It

The secondary regulator on that line has failed, or there’s a crack in that specific line. Isolate that line immediately (close the isolating valve to that keg if you have one). The other lines are fine. Call an engineer for that one line. Don’t keep pouring from it because you risk pushing uncontrolled pressure through a damaged line.

Excessive Foam on All Lines, Pressure Gauge Reads High

Your regulator is set too high or has drifted upward. Reduce the pressure slowly — turn the adjustment screw counter-clockwise by one quarter turn, wait 30 seconds, and test. Each line should stop foaming. If the gauge shows 4.0 bar and you need 3.0 bar, this is an easy fix. If it keeps drifting back up after you adjust it, the regulator spring is failing and you need a replacement.

CO2 Safety, Compliance and EHO Expectations

CO2 is a controlled substance under UK health and safety law. Your EHO inspector will check three things: that you have documented pressure checks, that your regulator is fit for purpose, and that your cellar is clean and organised around the equipment.

The HSE expects all pressure equipment to be certified and maintained by qualified engineers at intervals defined by the manufacturer. This usually means a full service every 12–18 months by a registered engineer (Gas Safe in most cases). When I prepared for my NSF audit in March 2026, the first question was: “When was the regulator last serviced?” I had the engineer’s certificate in a folder. That’s what they want to see.

You must also keep a record of all cylinder changes. Who changed it? What date? What pressure was it? This creates a chain of evidence if anything goes wrong. If a keg is damaged or product is wasted, you can show the auditor that the pressure was correct and the fault lay elsewhere.

If you’re tied to a pubco (Marston’s CRP, Greene King, Star, etc.), your BDM is responsible for major cellar equipment, but you are responsible for daily checks and documentation. Get clarity on this before you sign a tenancy. Some pubcos will replace a broken regulator; others will bill you for it. Tied agreements vary wildly.

For fire safety and risk assessments, CO2 cylinders must be stored safely in a dedicated area with good ventilation. A leaking CO2 cylinder in a sealed cellar is a suffocation risk. Your fire insurance and EHO will expect this to be correct.

CO2 System Costs and Who Pays

Understanding the true cost of CO2 systems is crucial if you’re taking on a pub. Here’s the breakdown:

Ongoing Costs (Your Responsibility)

• CO2 cylinder refills or exchange: £10–20 per cylinder (usually included in your tied beer tie if you buy from the pubco). A typical pub uses one 10kg cylinder per 2–3 weeks depending on volume.
• Pressure gauge check/replacement: £40–80 every 3–5 years or if faulty.
• Engineer call-out for leak investigation: £60–120 plus parts.
• Annual service of regulator: £100–180 (sometimes the pubco covers this, sometimes you do).

Annual pressure-related costs in a small 180-cover pub like Teal Farm: roughly £200–400 if nothing breaks, £600+ if you have a leak or a major component fails.

Capital Costs (Usually Pubco Responsibility, But Check)

• Regulator replacement: £200–350 fitted
• New pressure gauge: £60–100
• CO2 cylinder: £150–250 (though these are usually owned by the gas supplier)
• Secondary regulators (per line): £80–120 each
• Complete cellar pressure system overhaul: £1,500–3,000

When you’re taking on a tied pub, ask for a pre-ingoing cellar inspection. Get a Gas Safe engineer to assess the regulator and system. If it’s more than 10 years old, it’s likely due for replacement — and you don’t want that liability landing on you three months into your tenancy. Put it in writing before you sign.

Most tied agreements state that the pubco maintains the “primary” equipment (cylinders, main regulators, pipework) but you maintain the daily operation and checks. If the regulator is faulty, they fix it. If you ignore a pressure drift for six months and it causes a keg to explode, that’s on you.

Before you take on a pub, you need to understand your numbers clearly. Using a Pub Command Centre from day one gives you real-time visibility on how much each week’s wastage is costing you. At 180 covers, if you’re losing 2 kegs a month to pressure issues, that’s roughly £40–50 in direct loss plus the labour cost of troubleshooting. The tool costs £97 once and includes cellar tracking — you can log every pressure check, every keg change, every fault, all in one place. Most pub landlords guess at these numbers. You’ll know them precisely.

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