Hi,
I had an email from my tenants they have observed water leaking from the outside gutter when the shower is in use.  I am not able to verify this as I do not live there.  Using my physics background and a quick internet search that brought me here ...  I guess it could be pressure from the cold water feeding back up the hot water pipe, there is the downstairs kitchen faucet and showers upstairs and downstairs where the hot and cold water are joined, although I would have thought there were valves preventing this scenario. 

The upstairs shower was installed new 3 years ago, and is one of those that uses the Venturi Effect to increase hot water pressure in the low pressure gravity fed system.  I recently had the downstairs kitchen taps fixed (washers replaced) and they turned the hot water back down to 60 from 70.

Anyhow I have asked the tenants to test if the water in the gutter is hot, but otherwise they are not concerned...  Should I be, is this something to look at urgently or can it wait until I get back, or is it part of the way the Venturi works?  I would have thought a brand new shower would last a bit longer, or could it be the work in the kitchen that damaged it?  I will certainly call in a plumber if required or urgent, but after already paying a master plumber twice to change washers (which I have always done myself), I would rather wait until I get back later this year to investigate if it is not serious.

Craig

Linkback: https://www.plumbers.nz/q-and-a-baths-and-showers/64/overflow-leak-when-using-shower/641/

If you feel that you have been the victim of poor workmanship by a Master Plumber then you should definitely contact their CEO Fiona Gavriel as they have a formal complaints procedure and a Master Plumber Guarantee to back up the work of their members.  Master Plumbers advocates the highest standards of quality and they will, I am sure, be unhappy to hear that a member has not lived up to that.  Of course it is important to verify they are actually a member - and you can do this by calling their Wellington office.  I would encourage you to do so.

Thank you for the replies.  I had not intended to imply poor workmanship by the plumbers, just listing all other information that might have had an affect, or indicate a related problem.  If I sounded negative it was only frustration having to get in a tradesman to change washers because I am overseas! The tenants had no problems with the shower or hot water, and I am waiting to hear back if the water in the gutter is even hot.  All I know for sure is they think there is water coming off the roof each time they use the shower.   Since there appeared to be no negative impact I was planning to just monitor the situation until I get back, and I posted here to see if there was anything I was missing that was obvious to an experienced plumber, like "thats how it is supposed to work" (unlikely) or "your hot water cylinder is about to go into orbit" (also unlikely I hope with low pressure ...)

Thanks again for replies, this seems like an excellent forum to prevent DIY'ers like me from doing too much damage!

Cheers
Craig

That sounds a reasonable solution, I thought there would be pressure valves anyhow, however would this work with the Venturi Effect shower head as I thought this required higher pressure cold water to increase the hot water pressure in the shower?  If it was just a missing valve, then presumably this has been going on for a very long time without any serious consequences and is not urgent.

Cheers again

I have had cases like this before and the hot still comes through, just half as much depending on how far the push is. In this case I could also be wrong though Its easy to find out if you have equal or unequal pressure just turn hot and cold on. If the cold has more pressure then its unequal pressure. The limiting valve will only be on the hot.

Actually I think your right. So what else could cause the overflow when showering?

maybees the hot water in the vent pipe is set too close to the top of the pipe opening so when the shower is turrned on and the PRV activates the cold pressure is pushing/surging out through the vent pipe because the origional standing pressure has been set too close to the top of the vent???...sounds plausible???...one would think if the PRV was faulty it would continousley pass water...or as you say the water pressure is overcomming the hot and backfeeding into the cylinder...this is a tricky one to guess...Maybees this house has excessive mains pressure making the venturi mixer not function as it should?