Commercial Boiler Losing Pressure or Leaking?

Q: How do I book or get a quote?

Call 0800 0996 007, WhatsApp 07947 578332, or email estimates@fastcommercialboiler.help with the site, fuel and what you need. A photo of the pressure gauge, the pressurisation unit display and any fault code helps. Rates can be negotiated.

Why commercial systems lose pressure

Pressurisation unit faults: failed pump, pressure switch or break tank valve
Expansion vessel lost its charge or has a failed membrane
Leaking pump seals, valves, air vents or joints in the plant room
Leaking boiler heat exchanger or calorifier coil
Leaks out on the system: radiators, fan coils, underfloor mains
Safety valves lifting because the system is over-pressurising

Leak and flood make-safe

If water is coming into the plant room, isolate electrics only if it is safe, turn off the cold feed to the pressurisation unit if you know where it is, and call us. We isolate, contain and make safe first, then repair or replace the leaking component. We also handle commercial plumbing emergencies; see each town's emergency commercial plumber page from our locations list.

Constant topping-up adds fresh, oxygenated water that corrodes heat exchangers, so a slow leak is worth fixing properly. See also plant room repair and 24/7 emergency call-outs.

How a sealed commercial heating system holds its pressure

Most commercial heating systems are sealed: the water is not open to a tank in the roof, so the system needs three things working together to stay at the right pressure.

The pressurisation unit fills the system from a break tank and tops it up when the pressure falls below its set point. It has a pump, pressure switches or a transducer, and its own low and high pressure alarms.
The expansion vessel takes up the extra volume as the water heats up. It has a gas pre-charge on one side of a membrane, and if that charge is lost the system has nowhere to expand into.
The safety valves and the boilers' own pressure protection stop the system going too high, and lock the boilers out if the pressure drops too far.

The cold fill pressure has to suit the height of the building, because the water at the top of the system must stay above atmospheric pressure. That is why a multi-storey office, a hotel and a single-storey warehouse can all run at different pressures. If someone has changed the set points, or fitted a different vessel, the system can start losing water or locking out even though nothing is actually broken.

What the pressure is telling you

Slow fall over days: a small leak on the system, often a valve gland, an air vent, a radiator or fan coil connection, or a joint in a ceiling void.
High when hot, low when cold: expansion vessel pre-charge lost or a failed membrane, with the safety valve lifting at the top end.
Pressurisation unit running often: the system is losing water, or the unit's pressure switches have drifted and it is cycling. A water meter on the fill line shows how much is going in.
Break tank overflowing or empty: a stuck float valve or a failed fill solenoid on the pressurisation unit.
Low-pressure lockout after other work: air left in the system after it was emptied for other work, or a section not refilled and vented properly.
Water in the boiler casing or under the boiler: a leaking heat exchanger, seal or internal pipe, which should be looked at promptly because water and gas appliances do not mix.
Gauges disagreeing: the boiler gauge, the header gauge and the pressurisation unit should read close to each other once height is allowed for. A big difference often means a faulty gauge or sensor rather than a real pressure problem.

How we trace a leak or pressure fault

Phone triage. When you call 0800 0996 007 we ask what the gauges read, whether the pressurisation unit is showing an alarm, whether water is visible anywhere and what work has been done on the system recently.
Make safe. If water is coming into the plant room, the engineer isolates and contains it first and checks that boilers, pumps and controls are safe to run.
Check the pressure equipment. Expansion vessel pre-charge, pressurisation unit set points and alarms, fill solenoid and break tank, safety valves and gauges.
Isolate and watch. Where the leak is not obvious, sections of the system are isolated in turn and the pressure watched, so the search can be narrowed down to one circuit, floor or branch.
Repair, refill and vent. The faulty part is repaired or replaced, the system is refilled and vented, and the pressure is set to suit the building.
Record and advise. You get a note of what was found, the pressures and set points left on the system, and any follow-up work, such as water treatment after a large loss of water.

Engineers come from our team of over 10 local engineers, based at CO10 8NN near Sudbury and covering commercial sites across Suffolk, Essex and Cambridgeshire.

Why constant topping-up costs more than the leak

Every litre that leaks out is replaced with fresh mains water. That water carries dissolved oxygen, which drives corrosion and sludge, and hardness, which leaves scale on hot heat exchanger surfaces. It also dilutes the corrosion inhibitor that should be protecting the system. Over time that means blocked heat exchangers, failed pumps and more lockouts.

After a repair that has meant a lot of new water going in, it is worth checking the inhibitor level and water quality. Industry guidance such as BSRIA BG50 on water treatment for closed heating systems covers sampling and treatment. We can test and dose the system, or work alongside your water treatment contractor.

Safety and compliance

Gas safety: a leak inside a gas boiler can damage the burner, controls and flue components. Gas boilers are worked on under the Gas Safety (Installation and Use) Regulations 1998 by Gas Safe registered engineers, and all our gas work is carried out under registration 985448.
Pressure systems: some plant, such as steam boilers and high-temperature hot water systems, comes under the Pressure Systems Safety Regulations 2000 and needs a written scheme of examination. Your insurer or competent person will tell you if your system is covered, and we can work to that scheme.
Safety valves: safety valves should discharge to a safe, visible point. A valve that is lifting repeatedly is a symptom, not a fix, and should never be capped or plugged.
Water and electrics: plant rooms have pumps, controls and panels close to the pipework. If water is near electrical equipment, keep clear and only isolate the power if you can do so safely.

Repair or replace?

Most pressure faults are put right with a repair: recharging an expansion vessel, replacing a pressure switch, fill solenoid or pump on the pressurisation unit, or replacing a leaking valve, air vent or joint. Replacement is worth considering when an expansion vessel's membrane has failed, when a pressurisation unit is old and parts are hard to get, or when a boiler's heat exchanger has failed on an older boiler. In those cases we give you a written comparison of the options. For new boilers and larger plant changes, see commercial boiler installation and replacement, and for regular checks of the pressure equipment, see planned preventative maintenance.

Questions we get asked

Our commercial boiler keeps locking out on low pressure. What should we do?

Call us rather than repeatedly topping up. A repeat low-pressure lockout usually points to a leak somewhere on the system, an expansion vessel that has lost its charge, or a pressurisation unit fault. Each top-up adds fresh water that dilutes the inhibitor and brings in oxygen, so the sooner the cause is found, the less damage is done to the boilers and pipework.

How quickly should a sealed commercial heating system lose pressure?

A healthy sealed system should hold its pressure. Small changes as the water heats up and cools down are normal, but a steady fall from one day to the next, or a pressurisation unit that keeps starting to top the system up, means water is escaping somewhere and should be investigated.

The pressure shoots up when the heating is on and drops when it goes off. Why?

That pattern usually means the expansion vessel is not doing its job. Either it has lost its pre-charge or its membrane has failed, so there is nowhere for the expanded water to go. The pressure climbs until the safety valve lifts, water is lost, and the system is then low when it cools. We check and recharge the vessel, or replace it if the membrane has gone.

Can you find leaks that are not in the plant room?

Yes. Leaks are often out on the system rather than in the plant room: radiator valves, fan coil connections, air vents in ceiling voids, or heating mains under floors and in ducts. We isolate the system section by section and watch which part loses pressure, which narrows the search down before any floors or ceilings are opened up.

Is water dripping from a pipe outside the plant room a leak?

Not always. It may be a safety valve or an automatic air vent discharging through its pipework, which tells us the system is over-pressurising or has air problems. It still needs looking at, because the cause is usually an expansion vessel or pressurisation fault, and it can lead to low-pressure lockouts later.

Can a leaking boiler heat exchanger be repaired?

Leaking seals, gaskets and connections can usually be repaired. A heat exchanger that has corroded or cracked through normally has to be replaced, or on an older boiler it may make more sense to replace the boiler. We tell you which applies and give you the options in writing.

Do you attend plant-room floods out of hours?

Yes, 24 hours a day. Call 0800 0996 007 or WhatsApp 07947 578332. We make the plant room safe first and then repair or replace the leaking component.

Do you work on oil and LPG boiler systems with pressure problems?

Yes. Pressure and leak faults affect the water side of the system, whatever the fuel. Gas and LPG boilers are worked on under our Gas Safe registration, number 985448, and oil-fired plant by our OFTEC trained engineers.

How do I book or get a quote?

Call 0800 0996 007, WhatsApp 07947 578332, or email [email protected] with the site, fuel and what you need. A photo of the pressure gauge, the pressurisation unit display and any fault code helps. Rates can be negotiated.

Commercial boiler losing pressure or leaking