Ask a Tradesman
Placement of hot water tank in relation to a hot water pump
A plumber has replaced my negative head pump with a positive head one. In order to prevent another pump having to be bought, the landlord is authorising the following work:
Currently the hot water tank sits on the floor with the pump beside it, the cold water tank is raised as high as possible above this. The shower head is above the cold water tank, and the cold water tank cannot move any higher, therefore a negative system is needed. This is needed also as the other hot taps mix with the mains water not from the tank, and as the hot water tank is on the ground, it will not work with a positive pump. We currently have to run multiple taps in order to draw enough hot water through the pump in order to activate it.
The plumber is intending to place the hot water tank raised up where the cold water tank is, and then place the cold water tank on the floor. I do not think this will work as the cold water tank needs to flow down into the hot water tank.
I think that if the plumber does this the entire system will not work and we will be left without any water, so if anyone can give me an opinion on this that I can show the landlord, i can stop the work being done. As I am not a plumber my opinion is meaningless.
You are right, get another plumber.
Answered 2nd Nov 2014
I completely agree with Brown's - it's your plumber that requires replacement!
The position of the hot water cylinder is largely irrelevant. As long as your cold water tank is higher than your hot water outlet, your cylinder can go anywhere in between.
If you have a positive head pump now, and your landlord is unwilling to replace it for the negative head equivalent, you'll need a way of activating the pump. This is quite often done using a push button switch wired in parallel to the flow switch (it only needs wiring to one of them). The push button switch should be a 'normally open, momentary' type of switch. It's a bit of a nuisance, but you'll have to turn on your shower then push the button then the water will begin to flow. You should be aware that most of the pump manufacturers will not honour their guarantee once the pump has been adapted, Salamander won't even honour it if you don't feed the pump through an S-Flange or similar.
If you do as your landlord has authorised, and place your cylinder higher than the tank (a ridiculous thing to do!) then you will have no hot water at all, as the cylinder will not be able to fill. If, for whatever reason, it did manage to fill, then the tank will overflow as the cylinder empties back into it.
Overall, by far the simplest and cheapest resolution is to replace the pump with the correct version.
Answered 1st Feb 2015