Commercial hot water plant repair: calorifiers & plate heat exchangers

What we work on

• Direct gas-fired commercial storage water heaters
• Indirect calorifiers heated from the boiler plant
• Plate heat exchangers and gas water heat exchangers
• Secondary hot water circulation pumps, blending and thermostatic controls
• Leaking vessels, coils and heat exchangers

Typical faults

Burner lockout or ignition failure, thermostat or control faults, scaled heat exchangers in hard-water areas (common across East Anglia), failed secondary return pumps giving lukewarm water at the far end of the building, and leaking tanks or coils. Stored hot water should be kept at 60°C and distributed at 50°C or above for Legionella control, so we check temperatures as part of the repair.

Water heaters are central for hotels, pubs & restaurants, care homes and schools. For wider plant-room faults see plant room repair.

Why hot water plant is separate from space heating

Space-heating boilers warm radiators and air handlers; hot water plant — storage heaters, calorifiers and plate heat exchangers — serves kitchens, showers and washrooms. A building can have heating but no usable hot water, or the reverse. That is why we treat water heater faults on their own page. An annual commercial boiler service can cover both the boilers and the hot water plant on the same visit, so records stay together.

Types of commercial water heater we repair

• Direct gas-fired storage water heaters: a burner heats a stored volume of water, typically from around 150 to several hundred litres. Common in hotels, sports centres, schools and kitchens, and often installed in pairs or banks so one can be repaired while the other keeps the building supplied.
• Continuous-flow (instantaneous) gas water heaters: wall-hung units, often several linked together, that heat water only when an outlet is open. Faults are usually flow sensors, ignition, fans or scale in the heat exchanger.
• Indirect calorifiers: storage vessels heated by a coil from the boiler plant. If the boiler side is working but the hot water is not, the cause is often the primary pump, a motorised valve, the cylinder thermostat or a scaled coil.
• Plate heat exchangers: compact units that heat water on demand from boiler water. They are efficient but sensitive to hard water, so descaling or replacing the plate pack is a regular job.
• Vented and unvented systems: older buildings often have a vented cylinder fed from a cold water storage tank; newer installations are usually unvented and run at mains pressure, with extra safety devices that need checking.

We also work on oil-fired water heaters (OFTEC trained engineers) and LPG units. Common commercial makes include Andrews, Lochinvar, A.O. Smith, Rinnai and Hamworthy; see our commercial boiler brands page, or send us a photo of the data plate.

What the symptom usually tells us

• No hot water anywhere: burner lockout, ignition or flame-sensing failure, a tripped overheat stat, a gas supply problem, or on a calorifier no heat arriving from the boiler.
• Hot near the plant room, cool at distant outlets: secondary return pump, non-return valve or circulation balance.
• Runs out at peak times: reduced output from scale or a burner fault, or a heater that is now too small for the building.
• Rumbling, banging or crackling: scale building up on the base of the vessel or in the heat exchanger, very common with hard water across Suffolk, Essex and Cambridgeshire.
• Water at the tundish or a relief valve: an expansion or overheating problem on an unvented system, which should be looked at the same day.
• Rusty or discoloured hot water: often a worn sacrificial anode or internal corrosion of the vessel.
• Water too hot at the taps: a faulty thermostat or a failed thermostatic mixing valve, which is a scald risk in care homes and schools.

If you smell gas, turn off the gas supply at the emergency control valve if it is safe to do so, open doors and windows, and call the National Gas Emergency Service on 0800 111 999 before calling us.

How a water heater repair visit works

1. Phone triage. When you call 0800 0996 007 we ask what is happening, the make and model, any fault code and whether part of the building still has hot water. That helps the engineer bring the likely parts.
2. Safety checks first. The engineer checks the gas supply, the flue and ventilation, and the safety devices before running the heater.
3. Diagnosis. Burner and ignition checks, combustion analysis on gas units, thermostat and control tests, pump and valve checks, and stored and return water temperatures.
4. Repair or make safe. Most faults are fixed on the first visit where the part is available. If a part has to be ordered, we tell you how long it will take and whether a second heater or temporary measure can keep the site going.
5. Written record. You receive a note of what was found, what was done, the temperatures recorded and anything that needs planning, such as descaling or replacement.

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.

Safety and compliance for commercial hot water

• Gas safety: under the Gas Safety (Installation and Use) Regulations 1998, gas water heaters and their flues must be kept in a safe condition and worked on only by Gas Safe registered engineers. All our gas work is carried out under registration 985448, which you can check on the Gas Safe Register website.
• Legionella control: HSE guidance (ACoP L8 and HSG274 Part 2) expects stored hot water to be kept at 60°C or above and hot water outlets to reach at least 50°C within one minute (55°C in healthcare premises). A heater that cannot hold temperature puts that at risk, so we record temperatures on every visit for your water safety records.
• Unvented systems: unvented hot water storage over 15 litres comes under Part G3 of the Building Regulations and relies on a temperature and pressure relief valve, an expansion relief valve and an expansion vessel. These should be checked when the heater is serviced.
• Scald protection: where vulnerable people use the water, such as care home residents and young children, thermostatic mixing valves are normally fitted at outlets. They need regular testing so the stored water can stay hot while the water at the tap stays safe.

Repair or replace?

Most water heater faults are worth repairing: burners, ignition parts, thermostats, pumps, valves and anodes are all replaceable. Replacement starts to make sense when the storage vessel itself is leaking, when the heater is old and parts are hard to get, or when the building's hot water demand has grown beyond what the heater can supply. In those cases we give you a clear, written comparison of repair and replacement costs. For new heaters and larger plant changes, see commercial boiler installation and replacement.

In hard water areas, an annual service with a check of the anode and heat exchanger, and descaling when needed, is the simplest way to avoid breakdowns. Water heaters can be added to a planned maintenance schedule.

Calorifier repair: common faults and what we check

A calorifier is a large hot water storage vessel heated by a coil, a plate heat exchanger, an immersion element or a direct burner. Because it stores water at around 60°C and often supplies a whole building, a calorifier fault affects kitchens, showers, washrooms and, in care settings, residents. These are the faults we see most on calorifier repair visits:

• Slow recovery or lukewarm water: scale on the coil, a primary valve that no longer opens fully, a failed primary pump, or a thermostat reading low. We check the primary flow temperature and compare it with the stored water temperature before changing parts.
• Water too hot or temperature swinging: a sticking motorised valve, a failed control thermostat, or a sensor sitting out of its pocket. The high limit thermostat is checked at the same time, as it is a safety device.
• Discharge from the tundish or relief valve: on unvented systems, this usually means a failed expansion vessel, a faulty pressure reducing valve or a relief valve that has seen debris. It is a warning sign and should be looked at promptly rather than left to drip.
• Leaks: from gaskets, inspection hatches, valves and joints are normally repairable; a weep from the shell itself usually means the vessel is at the end of its life.
• Noise and sediment: knocking or rumbling usually points to scale and sludge at the base. Emptying and flushing the vessel, with a check of the anode where one is fitted, often puts this right.

We record temperatures at the calorifier, on the return and at the furthest outlets, so you have figures to put alongside your water hygiene records. If the boilers feeding an indirect calorifier are the real cause, we deal with them on the same visit; see plant room repair and expansion vessel and pressurisation unit checks.

Calorifier heat exchanger repair: coils, tube bundles and plate heat exchangers

Most calorifier repairs we are called to come back to the heat exchanger: the part that moves heat from the boiler water (or the burner, on a direct-fired unit) into the stored hot water. How it is repaired depends on what type it is, so it helps to know what is fitted before anyone opens it up.

Two signs point to a heat exchanger leak rather than a valve fault: the heating system needs regular top-ups for no obvious reason, or the hot water tastes or smells like heating water. Either one needs checking promptly, because water passing between the two sides is a hygiene risk as well as a plant fault.

Scale builds up fastest in hard water areas, and much of Suffolk, Essex and Cambridgeshire has hard water. Water treatment on the heating side matters too; our guide to closed system water treatment explains why dirty heating water shortens the life of coils and plates.

Planning a calorifier repair around a working building

Hotels, care homes and kitchens cannot simply go without hot water for a day. A calorifier repair is planned so the building keeps as much service as possible and the water is safe when it comes back:

• Before the visit: we ask for the make, model and size from the data plate, photos of the pipework and the last service or inspection record, so parts such as gaskets, valves and bundles can be ordered first.
• Keeping some hot water: where there are two calorifiers or a standby water heater, we work on one at a time. Where there is only one vessel, we agree the quietest time of day and give you the time the hot water will be off.
• Isolation and pressure: the vessel is isolated on both the primary (boiler) side and the hot water side and the pressure released before anything is opened. Unvented vessels have safety valves that are checked before the vessel goes back into use.
• Bringing it back into use: the vessel is refilled, vented and heated back up to its normal storage temperature, and your responsible person is told so any flushing or checks set out in your legionella risk assessment can be done and logged.
• The paperwork: you get a written record of what was found, what was replaced and the temperatures on handover, to keep with your water hygiene records.

Our guides to hot water temperatures for legionella control and pressure and temperature relief valve checks cover the safety side in more detail.

Questions we get asked

Related commercial services

• 24/7 emergency commercial boiler repair
• Commercial boiler servicing
• Commercial boiler installation & replacement
• Commercial gas safety inspections (CP12)
• Commercial gas engineer
• Plant room & boiler room repair
• Cascade & condensing boiler repair
• Pressure loss & leak repair
• Warm air & radiant heater repair
• Commercial boiler brands
• Planned preventative maintenance (PPM)
• Commercial oil boilers (OFTEC trained)
• Commercial LPG heating
• Sectors we work in
• All towns we cover