Dripping prv ? (Pressure Relief Valve)

It is essential that, on a sealed heating or unvented hot water system, any dripping PRV can be observed and that passing water is safely directed to a point of discharge. This can be difficult for installers working in landlocked or high-rise installations where points of termination can be limited to long individual runs down the inside (or outside?) of the building to a basement level gully.

The hotun dry trap tundish is fully compliant with building and water regulations. 

hotun differs from the traditional tundish as it eliminates foul odours from coming up from any connected drain without the risk of drying out associated with wet traps. This one-product solution solves many of the boiler or unvented water heater dripping PRV discharge routing issues that installers are commonly faced with.

If there is an internal, foul waste or soil pipe available near the boiler or unvented water heater, then using the hotun dry trap tundish could be your most cost-effective and compliant answer!

Dripping PRV discharge pipe routing issuesTypical standard open sided tundish picture

A traditional tundish allows water from a PRV to pass through the tundish and enables the user to observe this from its open-sided construction. Complications occur for installers in high rise and landlocked situations as they have few options to terminate the discharge pipe in a cost effective way.

If a standard tundish were to be fitted it cannot be routed to terminate to a foul waste or soil pipe as foul odours are able to travel back up to, and out of, the tundish to the inside of the building! A definite no, no in terms of regulatory compliance.

A wet trap cannot be used, as the infrequent operation of the PRV would allow the wet trap to dry out and it would then become ineffective! Traditionally a tundish with a separate type of dry trap valve would have been used.


Dripping PRV – The internal discharge one product Solution – how hotun stops odours

Professional dimensioned technical drawing of hotun 100C dry trap tundishhotun has been purposely designed to resolve these issues. It allows either a full flow or drips of water to pass into the D2 and also prevents smells from traveling back up from the connected drain.

The hotun dry trap tundish follows the same design as a standard tundish, with its open-sided construction, but hotun goes one step further, in that it includes a patented non-return valve.

This valve comprises a one-way sprung valve that closes shut to protect against odours and then, when water starts dripping and there is between 5ml and 30ml of water in the tundish, the sprung valve opens (we call this the trigger point) allowing the water to pass through to the drain

This benefits the homeowner because it still allows them to witness any passing water through the tundish and, probably, far more importantly, allows the user to see any water in the tundish even after the PRV has stopped dripping without any odours.

High Rise apartments and dripping PRV pressure relief valves – The solution

The hotun hiflo tundish in either the hotun 100 or hotun sf range can be used to help combat the limited PRV discharge options for installers working in landlocked or high-rise locations. It is now possible for the PRV discharge to be directly connected to the internal waste. For boilers an added advantage is that the condensate drain can also be connected below the tundish to provide a one pipe solution.

It is our belief that (for boilers) this is a far superior option that routing the PRV to the internal condensate trap (as some boilers are designed to do) as the dripping PRV can be easily seen without having to take the boiler case off.

Ideal Boilers give advice on how hotun can be used in one of their technical bulletins (AD 117)Ideal Boilers technical bulletin for combined PRV and condensate solution using hotun hiflo dry trap tundish

  1. Internal boiler condensate trap
  2. 21.5mm condensate pipe (must always Tee in below tundish outlet)
  3. 32 – 22mm rubber reducer
  4. Boiler pressure relief valve PRV
  5. 15mm Copper PRV discharge pipe
  6. hotun shield
  7. hotun hiflo (max 600mm from boiler)
  8. 32mm HDPE/PP waste pipe
  9. 32mm universal HDPE/PP waste T fitting


Alternatively, the hotun installation guidance tells you all you need to know.

hotun dry trap tundish installation and maintenance instructions guide document


Without a shadow of a doubt, hotun has become the industries go to, one-product solution for almost 8 years and was and still is known as the hotun revolution!