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By pikeman
Hi all

I recently carried out a bathroom refurb and fitted a new shower with standard mixer valve. The customer had complained about low hot water pressure on her previous shower and she asked me if i would fit a shower pump, not something i had done before and something i would normally sub out. However, i was struggling under time constraints and had to give it a go so fitted a slamander CT55+ extra pump soley on the 22mm hot feed from the cylinder, i appreciate in this arrangement it does the whole house and not just the shower. Its a Gravity fed system, with two large CW tanks, the cold from tank in loft direct to the shower and the HW feed from the pumped side. The HW cylinder is on a shelf at the back of the bathroom, so more or less about level with the shower and the pump is sited at the base of the cylinder. I have a good head of about 70 to 80cm from bottom of CW tanks to the top of shower head but the pump is hunting even without any other outlets open elsewhere in the house. Initially i thought it might be head pressure but im pretty sure that checks out so im struggling for where to go next. I might also add that i havent fitted a Surrey flange or similar and the pump is noisy but im not convinced that pump aeration is causing the hunting problem. Any help would be much appreciated. Thanks
User avatar
its sounding to me that you are getting bounce back in pressure and if experience recals, you perhaps should of fitted a neg pressure pump.
i had this after a builder installed on in a flat just about exactly as you describe and i was called in to investigate. i told them wrong pump fitted get them back to change it !!
may be possible cause also that it needs an anti syphon solution ie a rise in the pipe work from take off so the pump is always fed or a one way valve may improve it. take a good read on the fitting instructions it, the problem may become apparant. :)
By pikeman
Thanks Redshaw. I did consider the neg pressure pumps originally but all the dimensions and factors req'd for the positive pressure are fine, everything is below the CW tank and by some good distance. Do you think the pump could be pulling the water from the vent pipe and then from the top of the cylinder thus causing the hunting?
User avatar
pulling the water from the vent pipe and then from the top of the cylinder thus causing the hunting?

despite what it says, if its not connected with a surry etc and it hasnt got a min of 2-3m head thats what happens seen it many times.
when a neg head is put in all problems dissapear. fine when the cws is in the loft and the draw off has a good incline if you connect to that, sneeds about 35 degree angle.

perhaps some of the lads can emphasise as i have been away 3 weeks and switched off lol

i would tell customer its faulty and swap it out for a neghead
User avatar
By Best
Use Surrey or Warix flange (whatever one suits the hot pipe and vent pipe orientation connected to top of cylinder) to give air free supply.
Make sure cylinder has controlled heat to a maximum of 65 degrees.
You really got to do everything to the pump manufacturers instructions.

Cold tank needs to have large enough volume of water, ball valve is supposed to be opposite side of tank to outlets to pump and hot outlet needs drilled just above the level of the cold is drilled so the hot would stop first in an event of no water in cold tank to avoid risk of scalding, but difficult to do all that on an existing job.

A negative only head pump won’t start unless an outlet is opened, so worth thinking about.
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