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Hot Water Tank!


Installation Send us your service request

Pace Heating & Plumbing offer a repair and maintenance service for mains pressure, electric water heaters and an installation service for new systems. If you would like a quote for the installation of a mains pressure water heater,

If you are thinking of changing from a gravity hot water system to a mains pressure hot water system, the following information may be of interest to you.

Hot water systems explained
Traditionally the delivery of hot water to appliances in domestic properties relied on gravity. The pressure delivered at the tap or appliance relies on the height of the cold water tank above the highest outlet. This is usually the shower on the top floor of the property. With gravity systems you can notice the increase in water pressure if the shower head is held low down close to the shower tray.

Components of systems designed for use in gravity systems are not suitable for use in mains pressure systems. For example in addition to changing the hot water storage cylinder you may have to change the shower cartridge to enable it to cope with the increase in pressure.

There are two types of mains pressure hot water system

  • Unvented Mains Pressure
  • Vented Mains Pressure (Thermal Stores)

The term vented refers to whether the system is vented to atmosphere or closed to the atmosphere and therefore pressurised. It is because unvented systems are closed that special safety precautions have to be taken. Without these precautions water within the system could become over heated and over pressured with disastrous results.

Unvented Mains Pressure Systems Vs Thermal Store (Vented Mains Pressure Systems)

Unvented Mains Pressure

Thermal Store (vented mains pressure)

The positives

The positives

Mains pressure hot water to all taps

Mains pressure hot water to all taps

No tanks required, saving space in loft

No specialist installation requirements


Does not require an annual service


Building control does not need to be notified


No tanks required, saving space in loft

The negatives

Vented cylinder

Requires specialist installation

No risk of pressure build-up

Annual service required


External discharge pipework required

The negatives

Installation requires notification to Building Control

The negative aspects of thermal stores apply to all mains pressure water heaters

Properties with mains pressure water systems will have mains pressure at all taps and water appliances. This applies to both hot and cold water. This is achieved by taking the supply for the hot water directly from the incoming water supply. From this point on there are two sets of pipes in the property; one for hot water and one for cold. Both sets of pipes are directly connected to the main supply and both rely on the main supply for their pressure and flow. The cold pipework provides the supply to the cold water outlets, the other passes through the hot water cylinder and from there to the hot side of the system. A balanced system, where the hot and cold water are delivered at the same pressure, have the hot and cold water branches split after the pressure reduction valve. An unbalanced system will have the cold water supply branched off before the pressure reduction valve.

Visit the following pages for more information
Unvented water heaters
Thermal stores (Vented water heaters)

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Unit 9 370 Ilford Lane IG1 2LZ
Tel: 0207 183 2727 Mobile: 07956800132 Fax: 0871 288 2327 |

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