Viessmann combined PRV and condensate pipe

13 Apr 2012
Reaction score
United Kingdom
On most boilers I've seen, the PRV is routed through the outside wall and then back on itself, so if ever the boiler discharges any water via the PRV then you can see it.

The Viessmann range seem to combine the PRV and the condensate pipe into one, so how are you supposed to see if the PRV is discharging ? It seems you can install a tundish in the condensate pipe, but again, how can you differentiate. Also, unless you like a water feature in your house, why would you want a tundish on an internally routed visible condensate pipe that is constantly discharging whilst condensing?
Sponsored Links
Do the Atags still leak where the tube connects onto the outlet of the PRV when it has been operated?

I must admit that some tundish's are appalling, they do nothing but direct the flow out of the sides.

A leaking PRV as opposed to the condensate running, can be identified quite easily (I.e. Running condensate does not cause system pressure loss unless the primary heat exchanger has packed in). It can be proved physically in much the same way as a leaking Expansion Valve or T&PRV on an unvented system can be found.

Sponsored Links
On the more common 100 (domestic range), it is the WB1 'c' range (been on the UK market for some 12 moths only) that has the combined PRV/Condensate drain. (system and Combi types)

As per Dan, this is a reliable boiler, not seen any letting by on my installs (around 20 or so, mostly WB1'B')

If the prv is passing you'll run out of pressure quite simple really.

As a homeowner that is all u need to know.

As a gas engineer you'll figure out how to see if the prv is actually dripping

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local