Very intermittent brief loss of shower pressure
Before getting a local plumber involved, I'd very much appreciate some thoughts on potential causes of my issue. Thanks in advance.
1. When taking a long shower, there is an almost split second sudden drop in pressure (as if someone turned OFF the water supply then immediately turned back on, but even more brief than the time this would take). This is similar to the effect of flushing the toilet in the old days and having a split second of low pressure (but I don't get, for example, all HOT or all COLD, it is ALL the water going off like holding your hand in front of the spray for a second to simply "stop" the spray.
2. More details.
o This happens only once every 7 to 10 showers, not every time. When it happens, it doesn't feel like all cold or all hot remains, it is more like all water stops, but so briefly that the shower head is never completely off (that is, it kicks back in almost immediately). Otherwise all pressure in shower and rest of the house is very strong and consistent.
o If I try to create the problem by flushing toilet, turning on other taps, etc. I can't. That is, I do NOT lose any shower pressure from flushing toilets, running other taps.
o This is an old house, but all the plumbing was done from scratch about 2 years ago, including line to the street meter, new hot water heater (electric), gut renovation of bathroom/shower, new feed lines, fixtures, etc.
o Problem only appeared in the last month or so, but it is so intermittent, that it could have always been around and simply didn't happen while showering.
o I haven't noticed any loss of pressure when using kitchen or sink in bathroom, but then again, I'm never running these taps for as long as I run the shower.
Shower valve intermittant problem
I would also suspect an obstruction in the piping. In my opinion it is most probable that it is somewhere in the piping near the main service line. The reason I suspect this is because both hot and cold are affected. Hot and cold are both dependant upon the main service. It could be that your shower is a high volume user compaired to a faucet or toilet refilling. Especially if the flow restrictors have been removed from your shower. The valve is capable of high flow being rated at over 13 gallons per minute. It may take lot's of flow to trigger the obstruction to close. Try running all of your faucets and the shower at once. flush toilets too. If you can recreate the error while running lots of water, I think you have a problem somewhere in the main water service. If you can't get it to cause the problem anywhere but the shower, I believe you may have a delaminating shower hose. The Techniflex shower hose is many layered. If you have a kink internally it could be that high flow plus the heat of a long shower will allow it to collapse internally. If this is the case, or before you start taking your water service apart, call Hansgrohe at 800-334-0455 and ask for a replacement hose. They stand behind their products 100% and will send it to you at no charge under the warranty. I should know. I am the manager of Technical Service for them. There is no possibility that this is an error with the shower valve in my opinion.