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Pumps & Pressurisation Maintenance

Pressurisation Unit Maintenance Checklist

A maintenance and servicing checklist for pressurisation units covering pressure settings, pump operation, expansion vessel checks, and fill valve inspection — essential for sealed heating and cooling systems.

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Also available as editable Excel and Word — with asset, sign-off and findings columns.

What is a pressurisation unit maintenance checklist?

A pressurisation unit maintenance checklist is a structured list of the 15 preventive maintenance tasks — covering visual, functional, safety and record-keeping checks — that keep a pressurisation unit running safely and reliably. It groups routine checks by frequency, from daily inspections to annual servicing, so FM teams and building engineers can plan and evidence preventive maintenance.

Core pressurisation unit checks

  • Check the fill valve and strainer for blockages, scale or leaks
  • Check system pressure is within the set range on the pressure gauge (cold and hot)
  • Verify the pressure relief valve operates freely and is piped to a visible safe drain
  • Record system pressure (cold/hot), make-up water consumption, alarm test results and any adjustments

What is a pressurisation unit?

A pressurisation unit maintains the correct static pressure in a sealed heating or cooling system. It automatically adds water to compensate for minor losses and adjusts pressure as the system temperature changes. The unit typically includes a small pump, a pressure vessel, pressure switches, a fill valve, and a pressure gauge. Correct system pressure is essential to prevent boiling, cavitation, and air ingress.

In commercial buildings, pressurisation units are usually mounted in the plant room close to the boilers or chillers they protect. They draw from either the mains cold water supply via a fill valve, or — on systems where the system water is treated — from a break tank with an integral pump. The expansion vessel absorbs the volumetric change of the system water as it heats and cools, keeping the static pressure within the band set by the high-pressure and low-pressure switches.

From an FM perspective, the pressurisation unit is one of the few assets where the make-up water meter is the single most useful diagnostic. A rising trend means a leak somewhere in the system, even if no fault has yet been raised — and catching that early avoids the much larger cost of corroded pipework and failed valves further down the line. The most common service findings cluster around failed expansion vessel bladders, fill valves stuck open, and pressure switches drifting out of calibration.

This checklist is one of 27 in our plumbing and water system maintenance checklists, covering pressurisation units, booster sets, storage tanks, TMVs and water treatment — pressure, hygiene and legionella control.

Typical Pressurisation unit maintenance checklist

A practical starting point for planned preventive maintenance. Always refer to the manufacturer's O&M manual and site-specific requirements.

Pressurisation Unit maintenance checklist showing tasks such as check system pressure gauge reading and visual check for weeping joints, each with its service frequency
A preview of the Pressurisation unit maintenance checklist — the full 15-task routine, service frequencies and safety notes are below, free to download as a PDF.

Visual Checks

  • Check the fill valve and strainer for blockages, scale or leaks
  • Inspect pipework, unions and gauge tappings for leaks or weeping joints
  • Verify the break tank level, ball valve operation and overflow path (where fitted)
  • Inspect pump shaft seal for weeping or visible drips

Functional Checks

  • Check system pressure is within the set range on the pressure gauge (cold and hot)
  • Verify the pressurisation pump starts and stops at correct pressures (test by dropping pressure)
  • Test the low-pressure and high-pressure alarm functions and BMS notification
  • Inspect the pressure vessel pre-charge with a tyre gauge at the Schrader valve
  • Check the expansion vessel bladder by tapping — water in the gas side indicates failure
  • Check the water meter reading and trend make-up water consumption
  • Check pump motor current against the data plate FLA
  • Verify isolation valves on the unit operate freely and seat tight when closed

Safety Checks

  • Verify the pressure relief valve operates freely and is piped to a visible safe drain
  • Test the air gap and category 5 backflow protection on the mains feed (where applicable)

Record Keeping

  • Record system pressure (cold/hot), make-up water consumption, alarm test results and any adjustments

Download the free Pressurisation unit maintenance checklist PDF

Get all 15 tasks as a printable PDF — free, no signup needed. Keep a copy in the plant room, attach it to work orders, or share it with your maintenance contractor.

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PDF

The PDF is free and needs nothing. The Excel and Word versions add asset details, sign-off and findings columns so you can record the work as you do it — we ask for an email address for those.

Typical maintenance frequency

Suggested intervals for pressurisation unit maintenance. Actual frequencies should follow manufacturer guidance and site-specific risk assessments.

Weekly

  • •Check system pressure gauge reading
  • •Visual check for weeping joints

Monthly

  • •Record make-up water meter reading
  • •Trend make-up consumption against baseline

Quarterly

  • •Test alarm functions
  • •Check fill valve and strainer
  • •Cycle the pressurisation pump on test

Every 6 Months

  • •Expansion vessel pre-charge check
  • •Pump current and seal inspection
  • •Backflow protection test

Annually

  • •Full service including expansion vessel pre-charge top-up
  • •Pressure relief valve manual test
  • •Review make-up water consumption trend year-on-year
  • •Calibration check on pressure switches

Common faults and issues

Issues to be aware of when maintaining pressurisation unit equipment.

Excessive make-up water consumption indicating a system leak — water costs and corrosion damage compound
Failed expansion vessel bladder causing pressure fluctuations, water hammering and relief valve discharge
Pressure switch failure preventing the pump from operating or causing continuous running
Fill valve stuck open, continuously adding fresh water and over-pressurising the system
Low system pressure causing pump cavitation, boiler lockout and air ingress
Scaled or blocked fill valve strainer reducing the unit's ability to keep up with demand
Pump shaft seal weeping — small leaks build up over time and can mask larger system losses
Pre-charge pressure drift on the expansion vessel — even an intact bladder loses pressure over years
Backflow protection failure on the mains feed — a category 5 risk on heating/cooling system water
Pressure relief valve seat damage causing continuous discharge to the safe drain — usually after a high-pressure event

Safety and compliance notes

Key safety considerations for pressurisation unit maintenance. This is general guidance only — always follow OEM instructions, statutory requirements, and your organisation's safe systems of work.

Excessive make-up water is a warning sign — investigate system leaks promptly to prevent corrosion damage and dosing dilution
Pressure relief valves must discharge to a safe visible location — do not block or cap the discharge
Isolate the mains water supply before servicing the fill valve or break tank
Do not adjust pressure setpoints without understanding the system design parameters and the height of the highest emitter
Treat the gas side of expansion vessels with care — stored pressure can release the Schrader valve under load
Where a category 5 backflow risk exists, only competent water hygiene contractors should modify the fill arrangement

Reference standards and frameworks

United Kingdom
SFG20 schedules and CIBSE Guide M
North America
ASHRAE/ACCA Standard 180 and Hydraulic Institute maintenance guidance

Frameworks commonly referenced when planning pressurisation unit maintenance programmes. Always confirm the requirements that apply to your site and jurisdiction.

How PM Assist helps

Managing Pressurisation unit documentation with PM Assist

PM Assist helps FM and building operations teams search their O&M manuals and building drawings in seconds. Upload your pressurisation unit documentation and ask questions like “What is the design duty point?” or “When were the pump seals last replaced?” — and get source-cited answers instantly.

The checklist tells you what to check. The manual tells you the numbers.

Ask a pressurisation unit manual a question and get the answer back with the page it came from. No signup, and you can drop in your own PDF instead of the sample.

“What is the design duty point?”

Runs against a sample chiller manual so you can see the shape of the answer — then try it on one of yours.

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Further reading on pressurisation unit maintenance

Reactive vs Planned Maintenance Explained·The Problem with Traditional O&M Packs·Why Building Engineers Waste Hours Searching Documentation·All articles

Compliance topics for pressurisation unit maintenance

SFG20 Explained: The Standard for Building Maintenance·Planned Preventive Maintenance (PPM) Explained·Legionella Control & ACoP L8 Explained·PUWER Explained: The Work Equipment Regulations·All topics

Related guides

Find Equipment Specifications Across Building Documents·Find Maintenance Schedules in O&M Manuals·Search Drawings & Technical Documents with AI·Planned Preventive Maintenance Documentation·All guides·UK facilities management statistics

Compliance & CAFM

Run pressurisation unit maintenance in PM Assist

This checklist is also a planned maintenance programme in PM Assist, included in every paid plan alongside the compliance register and mobile inspections.

  • Add a pressurisation unit to a building's asset register and this maintenance programme is created for you, with each task on its frequency in the planner.
  • Visits are logged with notes and certificates, and overdue work is flagged before it becomes a finding.
  • Contractors can be given a login to see their jobs and upload certificates.
See the compliance and PPM softwareCompare plans

Frequently asked questions

What should the pressure be on a pressurisation unit?
The correct system pressure depends on the building height and system design. As a guide, the minimum cold fill pressure should be enough to push water to the highest point of the system plus a margin (typically 0.5–1.0 bar above the static head). The operating pressure will be higher when the system is hot. Check the commissioning records for the specific setpoints. For a typical 6-storey UK commercial building, cold fill is often 1.5–2.5 bar at the plant-room gauge.
Why does my system keep losing pressure?
Persistent pressure loss indicates a leak somewhere in the system. Common locations include valve glands, radiator connections, air vents left open, failed safety valves, underground pipework, and weeping unions on the pressurisation unit itself. Monitor the make-up water meter — a rising consumption trend confirms a leak even if you cannot find it visually. On large systems a hidden leak of 5–10 litres per day can run for months without being noticed at the gauge.
How do I check a pressurisation unit expansion vessel?
Isolate the vessel from the system, drain the water side, and check the gas pre-charge pressure with a tyre gauge at the Schrader valve. The pre-charge should match the system cold fill pressure minus about 0.2 bar. If the vessel is waterlogged (water comes from the Schrader valve), the bladder has failed and the vessel needs replacing — the unit will keep losing pressure on cooldown until it is changed.
Is this checklist relevant for 'pressurization unit' maintenance (US spelling)?
Yes — pressurisation unit (UK spelling) and pressurization unit (US spelling) refer to the same equipment. The checklist tasks, service intervals, and fault symptoms are identical regardless of spelling convention. The equipment maintains correct static pressure in a sealed heating or cooling system through a small pump, pressure vessel, pressure switches, and fill valve.
How often should pressurisation unit servicing be done?
Weekly visual pressure-gauge checks by site staff, monthly make-up water trending, quarterly alarm and pump cycle tests, and a full annual service that includes expansion vessel pre-charge check, pressure relief valve manual test, fill valve strainer clean, and a year-on-year review of make-up water consumption. Mid-life pressurisation sets benefit from a biannual pump seal inspection — a small drip becomes a costly seal failure if missed.
What's the difference between a pressurisation unit and a pressurisation set?
A pressurisation unit is the standalone make-up assembly — pump, vessel, switches, fill valve — that maintains the static pressure of a sealed system. A pressurisation set is the more general term often used for the same assembly when supplied as part of a larger packaged plant-room solution. In a commercial building they refer to broadly the same equipment; the term used usually follows the manufacturer's catalogue.
How much does pressurisation unit maintenance cost per year in the UK?
A standalone pressurisation unit added to a wider plant-room PPM contract typically adds £150–£350 per year for the structured quarterly checks and annual service. Reactive call-outs are usually £180–£300 per visit before parts. The biggest hidden cost is the make-up water itself if a slow leak goes undetected — a 10 l/day loss is around £50–£100 per year in water alone, but the bigger cost is the corrosion and inhibitor dilution it drives.
Why is my pressurisation pump running constantly?
A constantly-running pressurisation pump almost always means one of three things: a significant system leak the unit is trying to compensate for; a failed expansion vessel bladder so the unit cycles on every thermal contraction; or a stuck or failed pressure switch that is keeping the pump enabled. Check the make-up water meter first — if it is climbing, you have a leak; if it isn't, suspect the expansion vessel or pressure switch.
Does the pressurisation unit need to be on the BMS?
Pressurisation units do not have to be BMS-integrated, but doing so is strongly recommended in commercial buildings. BMS integration allows real-time alarms on low/high pressure, trending of system pressure across the heating season, and meter-based make-up water alarms that catch leaks days or weeks earlier than visual inspection alone. On a modern plant-room install, a minimum integration set is high-pressure alarm, low-pressure alarm, pump-run status and make-up meter pulse.
What happens if a pressurisation unit fails completely?
On a sealed heating system, a failed pressurisation unit will eventually lead to low-pressure boiler lockout and loss of heating, with secondary risks of pump cavitation, air ingress and inhibitor exhaustion. On a chilled water system, the same low-pressure path leads to chiller flow faults and possible freeze trips. Plant rooms with critical systems should have either redundant pressurisation units in parallel, or a documented manual fill procedure for use during failure.
What's typical make-up water consumption for a commercial heating system?
A well-sealed commercial heating system loses very little water — well under 1% of system volume per year on a healthy install. For example, a 5,000-litre system might use 30–50 litres a year of make-up. Consumption above ~5% per year warrants investigation; above ~10% per year usually indicates an active leak that needs locating before corrosion damage compounds.
Can I increase the cold fill pressure to fix a low-pressure trip?
Almost never the right first move. Raising the cold fill setpoint masks the symptom of a leak or failed vessel and risks over-pressurising the system once it warms. Always investigate why the pressure is dropping first — check the make-up meter, the expansion vessel pre-charge, and the relief valve discharge for evidence of cycling. Only adjust the setpoint after the underlying cause is identified, and within the system's design pressure envelope.
What does a pressurisation unit do?
A pressurisation unit keeps a sealed heating or chilled water system at the correct static pressure. When the system cools and contracts, or loses a little water through a weeping gland or an air vent, the pressure at the top of the building would otherwise fall below the point where the highest emitters or the boiler flow switch see enough head — so the unit tops it up. It replaces the old open feed-and-expansion tank: instead of a cistern in the roof, a small pump and break tank in the plant room add water on demand, and an expansion vessel absorbs the volume change as the system heats.
How does a pressurisation unit work?
The unit sits on the system return with a pressure sensor or switch watching the system pressure. When the pressure drops to the low setpoint, the fill pump runs and pushes mains-quality water from the break tank through a non-return valve into the system until it reaches the cut-out pressure; a type AB air gap in the break tank keeps the system water from backflowing into the mains supply (a WRAS requirement). The expansion vessel does the reverse job — its pre-charged air side compresses as the water expands on heat-up, so the pressure rises smoothly rather than lifting the safety valve. High- and low-pressure switches raise alarms, usually to the BMS, when the system drifts outside the design window. Servicing, in short, is checking that each of those parts still does its job: the sensor reads true, the pump fills, the NRV holds, the vessel still has its pre-charge and the alarms still trip.
What does pressurisation unit servicing involve, and when is it a repair job?
A routine service covers: checking system pressure cold and hot against the commissioning setpoints; testing the fill pump runs and stops at its cut-in and cut-out pressures; inspecting the break tank, float valve and air gap; cleaning the fill line strainer; verifying the expansion vessel pre-charge with the vessel isolated and drained; manually lifting the safety valve; testing the high- and low-pressure alarms through to the BMS; and reading the make-up water meter against the last visit. It becomes a repair when something fails those checks — the usual culprits are a waterlogged expansion vessel (bladder failed), a pump that runs but cannot reach pressure (worn impeller or passing NRV), a pressure transducer reading low, or a float valve letting the break tank overflow. Most are same-day fixes with the right spares; a controller fault on a packaged set usually needs the manufacturer's service partner.

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