The water storage tank is an essential part of your building’s complete heating, ventilation, air conditioning (HVAC) and water services system.

By extension, a ballcock is an essential component in the system, as its job is to regulate the water level in the tank. The tank then provides water to what are known as domestic services – toilets, taps and sinks – in both commercial and domestic premises. It also acts as a back-up supply in the event of interruption to your mains water supply. Therefore, the water tank plays a key role in ensuring the smooth day-to-day operation of your building.

Recently, we received a callout about a water leak on the floor of a plantroom. View below video for the Thermodial service engineer’s investigation, diagnosis and solution.

The role of the service engineer and facility manager

The video displays the importance of persisting in following an issue to a satisfactory engineering solution – uncovering the slits in the valve – rather than a cosmetic one.

One of the dangers in this situation would have been if someone had mopped up the water in the plantroom and not reported it. Thankfully the local facility manager realised the potential danger and averted further overflows by calling in a HVAC service engineer.

Water tanks

It is essential that water tanks are included as part of a planned preventative maintenance (PPM) regime not least because of the potential destructive nature of a water leak, but also for health reasons, protecting building occupants through legionella control.

With a lot of water tanks located at the top of buildings, mains water is often piped up to the tank at high pressure, meaning any failure in that tank system could lead to leakages and the continuous out-flow of water at high-pressure. This could cause catastrophic water damage, ruining a building interior and its contents.


Ballcocks are float devices that control the water flow into water tanks and cisterns.

Once water enters a tank or cistern through a valve, the water level rises and thus the floating ballcock rises. Once the ballcock float rises sufficiently, it seals the valve shut, stopping any further water from entering.

The tank may overflow, like in the above video if the ballcock fails due to:

1. A slit in the valve
2. The rubber washer on the valve deteriorating and failing to seal shut
3. Dirt entering the valve and failing to seal shut
4. The ballcock no longer floating, having taken on water

Planned preventative maintenance (PPM)

PPM of water storage tanks should take place as part of a building’s complete HVAC and water services system due to their interconnecting parts. View further information on HVAC and water services maintenance.