Hot Water Boost Pump Problems With Gravity Fed System


Postby andycain » Tue Jul 31, 2018 11:05 pm

Good evening all. I'm hoping someone may be able to help me!

Firstly, I'd like to say I'm competent with nearly all things DIY including plumbing however this problem has stumped me.

My father-in-law to be now thinks I'm an idiot as we are having an ongoing issue in his house with his hot water supply. He was complaining about low pressure on his kitchen mixer tap on the hot side which is a gravity fed system from his hot water tank. The cold side is fed from the cold main. I offered to buy him a pump and fit it. I bought a Salamander Pump and an S Flange for the top of the tank. When I went to fit it, it turned out it was a cheap tank with only a 22mm threaded outlet on top. Not wanting to fit an Essex-valve, I returned the S flange and installed the pump between the outlet / vent pipe and the feed to the taps in the rest of the house. I did this all in 22mm copper, no flexi pipes or pushfits other than the flexi hoses that came with the pump. After doing this, everything was beautfiul. Lovely high pressure hot water....for about 2 days.

This is where the trouble started. The performance of the pump seemed to dip ever so slightly but still engages as expected upon opening any of the hot taps in the house except for the kitchen mixer tap which did work initially. When turning the mixer tap to hot, the pump does not engage as it did intially and the water barely trickles out, significantly worse than before I installed the pump. I believe the pump is fine as every other tap works flawlessly. I initially expected an airlock, so I tried everything I could to remove it but to no avail. If I disconnect the hot supply from the problem tap and open the isolator valve, the pump engages and pressure is good at the feed, just before it enters the tap. If I swap the hot side of the mixer to the cold mains, water flow is good as well. To me, this rules out any issues of blockages. The tap uses 10 (maybe 13mm) flexi connectors, either way, less than 15mm. Is it likely that this is the cause of the problem? They're very thin and to be honest I hate them! Is this causing too much of a restriction for the pump? As I said, this all worked fine to begin with but now it's pants! How can the tap be peforming worse now it's at a higher pressure than it did before under gravity alone and why would this all work fine and then suddenly fail on a single tap?

I'm at a complete loss now and my father in law thinks I'm an idiot!! Haha. Any help would be most appreciated!
andycain
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Postby harrisjohnpaul » Fri Aug 03, 2018 5:54 am

Ok, it's easy for air to get locked when you run it off the vent pipe.

It's when people run different taps it seems to trap air in the pump.

Can't you just put an Deleted flange in. They can be tricky as you don't want to drop the washers into bottom of cylinder but a steady hand you should be fine.
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Postby andycain » Wed Aug 08, 2018 10:00 am

Yes I've had a look at Deleted flanges. Doesn't look too bad. Thanks for your help!
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Postby harrisjohnpaul » Thu Aug 09, 2018 9:18 am

Deleted flanges are slightly better
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