hotun detect by RA Tech


Pressure Relief Valve warning now has audible alerts – The key to alerting the user to the presence of unwanted water!


hotun detect – It makes hotun sense


hotun detect launch announced

Dripping Pressure Relief Valve water is one of the most misunderstood warning signs that an appliance is going wrong. hotun detect is the world’s first in-tundish water detection and temperature sensing, audible and visual alarm system. It will automatically alert the homeowner if there is water dripping out of the boiler or unvented water heater Pressure Relief Valve.

RA Tech UK Ltd are therefore proud to launch their latest innovation and a world’s first!

What is hotun detect?

hotun detect is a unique product that not only detects dripping Pressure Relief Valve water passing from a boiler or unvented hot water heater, through the tundish, but it also senses the temperature of the water. It has four stages of alarm depending on the temperature of the water

hotun detect automatically alerts the user when water is dripping from a Pressure Relief Valve

It uniquely moves the hotun tundish from a passive warning to an active warning system. Water passing out of the Temperature and/or Pressure Relief Valve (T/PRV) and through the hotun dry trap tundish is brought to the homeowners or building users attention via the audible and visual alarm.

This active warning gives an early alert of any problems with boilers, hot water cylinders, or systems that hotun detect is fitted to.

Problems overcome vs standard tundish

It will overcome many of the shortcomings that a standard tundish has:

  • Passive warning. Dripping Pressure relief valve water through a tundish (or out of a boiler a PRV discharge pipe) goes largely unnoticed and/or ignored until it is too late. A boiler can lockout (caused by low pressure) and/or many liters of water is wasted (unvented water heater) as well as wasting the energy needed to heat that water!
  • Preventing the buildup of limescale. Water dripping, unnoticed, through an unvented T/PRV discharge, causes a build-up of limescale. This can lead to water tracking over the sides of the tundish and causing damage to the floor near the tundish.
  • Discharging/dripping water at high temperatures is a risk of scalding. The audible (staged) alert gives the homeowner/user the information that there is a risk and they can then take the appropriate, prompt, remedial action.

What Pressure Relief Valve is hotun detect most useful for?

1/ BoilersPressure Relief Valve discharging to a hotun dry trap tundish from a boiler

There are some typical reasons why water discharges from a boiler Pressure Relief Valve.

a) The filling loop may have been left attached and water is coming into the heating circuit, causing it to go overpressure (3 bar)

b) The expansion vessel could have failed or lost its pre-charge pressure. It now no longer has the capacity to absorb the expansion of water as it heats up from ambient to system set point. The system pressure would then would climb to 3 bar whereupon the PRV would start to discharge water.

c) There could be a pinhole in the heat exchanger or the diverter block is allowing pressure from the cold water into the heating circuit.

This over pressurises the heating water above 3bar and is discharged out of the PRV

Technical bulletins from Worcester Bosch boilers covers the hotun tundish as acceptable for use, please download articles TB0121 and TB 0107

hotun detect can help

With the temperature sensing mode of hotun detect, the temperature of the water dripping through will give an indication of one of the above faults.

hotun detect in tundish alarm unit will alert the user to any water dripping from a Pressure Relief Valve on a boiler or unvented hot water heaterFor the engineer looking at fixing the issue, this additional information can be invaluable in order to correctly diagnose the problem. This increases the chance to provide a first-time fix, saving wasted time to go and get parts.

For the homeowner, the active early warning that hotun detect provides, means that fixing the boiler will be done before it shuts down on low pressure. In the case of b) above, meaning no inconvenient boiler breakdowns just when you don’t need it. It also means that the repair can be carried out as a planned visit for the engineer rather than a more expensive emergency call out.


2/ Unvented hot water heaters

Water discharging through ANY tundish is a warning that there is something wrong with the system it is attached to. Whilst unvented water heaters will not cut out (due to low pressures like the boiler above) if the PRV starts dripping and drips unnoticed, it will go on to waste a lot of water and the energy to heat that wasted water!

Typical reasons why an unvented cylinder’s Temperature / Pressure Relief Valve will start dripping

a) Either the expansion vessel has lost its pre-charge or has failed, or (on air bubble types) the air bubble is in need of replenishing.

When this happens, Typical installation arrangement for a hotun dry trap tundsih on large unvented cylinderas the water in the cylinder heats up, it cannot expand and the pressure rises (sometimes quite considerably, maybe even as much as 10bar) and the PRV, on the cylinder, opens to relieve the pressure (opening a tap would also relieve the pressure but that would happen by coincidence rather than design). This release of water will happen each time after water is drawn off and the cylinder re-heats, this can lead to a considerable amount of water wastage and the energy needed to heat the water going to drain

b) The inlet control group pressure reducing valve has failed in some way (or has been incorrectly set) and is allowing an excessive amount of pressure from the mains water to enter into the water heater.

In this instance, the water will be released at 3bar from the inlet control group PRV

c) There has been a failure of the heat input device (indirect wet coil or electric immersion heater) and the water in the cylinder is being overheated.

When the cylinder gets to 90°C the TPR (temperature relief valve) opens to allow cold water into the cylinder to ensure that the water in the cylinder does not reach 100°C. It does this by discharging the very hot water down to drain via the tundish. Large volumes of water are released in this failure mode and it is for this reason that the correct grade of waste pipe is specified and correctly fitted.

hotun detect can help

As with the boiler, the level of alarm can help with triaging the issue

A stage 1 warning (0 – 20°C) would normally indicate an inlet control group PRV discharge issue as this water will always be quite cool.

Stage 2 (21 – 60°C) would normally be water discharging from the cylinder itself (at the cylinder set point)

Stage 3 (61 – 85°C) indicates an early critical alert, telling the homeowner/end-user that the water coming from the Pressure Relief Valve is above any cylinder set point

The stage 4 critical alarm (86°C and above) provides an indication that the electric immersion coil ‘stat and overheat ‘stat has failed catastrophically

In all instances, if water from the unvented cylinder starts discharging via the T/PRV or PRV it will inevitably lead to a build-up of limescale in the tundish. Having the alarm sound draws the attention of the warning to the home/building owner/user so they can call in a plumber to further make a diagnosis and thereafter make effective repairs

The benefits of fitting hotun detect

  • An audible and visual alarm, actively tells the customer that there is something wrong so they are motivated to do something about it in a timely manner
  • The customer can make savings on the water which would otherwise have been lost “down the drain” unnecessarily
  • By alerting the customer to water dripping through the tundish, they can prevent the build-up of limescale by making timely repairs
  • Meets with G3 guidance Para 3.55 for persons with visually or mobility impairments
  • If the alarm is activated, the case for regular maintenance can be raised by the plumber with the customer, potentially leading to more work for the plumber
  • Simple, quick, hook-on design, makes fitting hotun detect really easy and requires no specialist electrical knowledge