Unvented HW Cylinder

[Johntheo5]

This is the approx 25 litre unvented cylinder that was in my Hotel Apartment (in a annex), in a well known European holiday country, all the other apartments were similarly equipped, power supply from a 3 pin plug (at least mine was), the only form of protection is the PRV shown, presumably a hi limit stat is incorporated in the Immersion, I have seen 5/10L undersink heaters with a PRV like this here at home but nothing as large as this, are these type of heaters legal up to a certrain capacity in the UK?.

 

[Madrab]

Sorry @Johntheo5 was there meant to be a pic to accompany this? PRV as in a Pressure Relief Valve?

You can get up to 30L undersink UV heaters using 3Kw here in the UK.

e.g. - Ariston Andris

 

[Johntheo5]

I,ve just added it as my first one was sideways!. are you saying up to 30L can be installed with a PRV just like the one above, in the UK?.

 

[Mottie]

I'm sure we had one much bigger than that in our villa in Spain.

 

[Madrab]

Wouldn't be quite like that no - UK's installs are a little more safety conscious, the PRV would either be on the hard pipe feed to the heater, (edit) flexi's wouldn't be allowed, or it would be incorporated with a mini EV if the non interrupted supply pipe isn't long enough to allow for expansion. The 30L ones would usually ship with a TPRV too, usually on the vessel itself.

 

[Johntheo5]

A friend of mine who had a 10L UV cylinder equipped with a Ariston 571730 PRV (like the one in the photo) and he noticed that, from time to time the PRV would have lifted and couldn't figure out what the problem was, he replaced the PRV, same problem, I gave him the loan of a pressure gauge which he attached to the HW outlet, pressure was ~ 2.5bar with a cold cylinder but within 10 minutes or so after the start of reheating the PRV started lifting at 8.5bar, on investigation, he found that the previous owner had installed a NRV on the mains, cylinder located ~ 15/20 meters downstream of this, he obviously removed the NRV, problem solved but noticed that the pressure would still rise by ~ 0.5/0.8bar on reheating. I took the old PRV apart and found it quite interesting, it was/is a combination valve with a PRV, NRV and anti syphon valve, the PRV portion is obviously allways opened to the cylinder, the NRV opens inwards to admit cold water and the anti syphon valve is a "mini" NRV inside the larger NRV but opens outwards, quite clever?, presumably to prevent the whole HW contents draining into the cold mains in the event of the mains supply failing or someone isolating the mains to do some work in the house.

 

[Madrab]

the previous owner had installed a NRV on the mains, cylinder located ~ 15/20 meters downstream

With the UK standards, using the supply pipe for expansion all depends on the size and length of pipe back to the nearest draw off point and no, check valves would normally be left out of the circuit unless a mini EV was fitted.

 

[polesapart]

I,ve just added it as my first one was sideways!. are you saying up to 30L can be installed with a PRV just like the one above, in the UK?.

15 litres is the UK maximum size. Above that requires installation with the full unvented safety group, discharge pipe and expansion vessel, and should only be undertaken by a G3 qualified engineer.

https://assets.publishing.service.gov.uk/media/5a80092540f0b623026911f3/BR_PDF_AD_G_2015_with_2016_amendments.pdf

Section 3.19