water supply to shower pump

[newplumb]

Is it ok to tee off from the pipe which supplies the hot water cylinder, and then connect that pipe to cold water inlet to pump. seems easier than putting new pipe in from atic just to supply pump.. probably reason why i should not but cant think why. thank you

 

[ChrisR]

It will interfere with other cold taps. You might get away with it, it depends how far, pipe sizes etc.

 

[kevplumb]

dont do it you will starve the cylinder ,think about it cylinder fed by gravity and you are pulling out of the inlet with a pump the pump wins you will probably pull hot water down the cold feed

 

[newplumb]

Thanks. I will come from tank, but I have a problem ,on pump instructions it says outlet from tank to pump should be a min of 30mm below the outlet which feeds the cylinder. I cant do that as the pipe which feeds the cylinder is right at the bottom of the tank so cant put new outlet below it. (My tank is round, thought this might make a difference)
Will it matter and if it does why? Thanks for any replies.

 

[ChrisR]

Idea is that the hot water runs out first so the shower goes cold not hot. Raise the HW takeoff?

 

[PEDANTICVINDICTIVEMAN]

Mmmmmmm, if it was me and the pump isn't a mega powerful type I would risk coming off the cold feed, I have had big problems with one of those round tanks splitting when they get older when drilling a new hole, the damn thing didn't leak until two days later and damaged the ceiling.
Try it off the cold feed first, if ok no worries, if not nothing lost, cap off, but you will then have to drill the tank, but be careful and keep an eye on it for a day or two.

 

[ChrisR]

one of those round tanks splitting when they get older when drilling a new hole, the damn thing didn't leak until two days later

INteresting! That's only the second time I've heard of that happening but it means I shall never do it again. Thanks PVM, I knew there was a reason why I read these forums!

You'd want a tap (full flow ball valve would be best) on the branch so you could just leave it there if it didn't work. Nearer the cistern the better.

 

[newplumb]

Idea is that the hot water runs out first so the shower goes cold not hot. Raise the HW takeoff?

As the shower is thermostatic and cuts off if there is a water failure from hot or cold, surely it wont matter if the feed to cold is higher in tank than feed to hot?


havn't decided what to do but both pump and showers guaratees are voided if you dont come from tank

 

[AdamW]

Even if you don't have problems from doing this, the pump will work at its best when working off separate supplies. You might even find that using a pump to boost what is essentially a single gravity fed pipe gives no better performance than the existing two individual gravity fed pipes.

If you are going to the expense and effort of installing a pump to boost your shower, you might as well get the full benefit of it.