Advice replacing old negative head pump

[Tykey]

Hi all,

My hot water pump has given up the ghost, so I need to replace it, but looking for a bit of advice as what replacement to go with.

This is how my system is set up: I have a cold tank in the loft, a Main System 18 HE boiler in the kitchen supplying hot water to a cylinder in the airing cupboard in the first floor main bathroom. Attached to this cylinder is a Salamander ESP80CPV which is the one that's died.

This pump supplies hot water to the kitchen tap, downstairs toilet sink, main bathroom sink and bath (not the shower which is an Aqualisa Digital Quartz Pumped - also in the loft) and en suite sink and thermostatic shower.

So here are my questions:

My understanding is that my current pump is a negative head pump. Is there any reason why this would have been installed rather than a normal positive head pump?

Should I replace like-for-like with another negative head pump, or could I save some money and go for a positive head one (which I gather are generally cheaper)?

Finally, I hear good things about Stuart Turner pumps? Based on my system, what would be a good one to go for?

Hope I've provided enough details for advice/suggestions. Thanks in advance.

 

[Madrab]

Where is the pump currently located? Is there a reasonable flow at the outlets on the same floor as the pump, with the pump off, and does some of the supply pipework rise up and over to the upstairs outlets?

ST pumps are what to fit IMO, a 2 bar single ST monsoon would be my suggestion.

 

[Tykey]

Thanks for your reply Madrab.

The pump is currently at the base of the cylinder (airing cupboard in upstairs main bathroom). The flow from the outlets is adequate to get by without the pump, but upstairs it takes an age to fill a bath for example, or downstairs even a bowl for washing up in the kitchen takes a while.

As far as I can tell, the only supply pipework that runs upwards is that to the pumped aqualisa shower. That goes to the processor box in the loft, but as this has its own pump I presume it's not affected by the main pump? Just guessing there though.

The only other one I'm not 100% on is the supply to the en-suite shower. That shower has never worked since moving into the house a few months ago (dodgy thermostatic cartridge I think, as it only runs cold). That pipework is all hidden behind the walls and we plan on ripping it all out and doing a new en suite in the next couple of months anyway.

 

[Madrab]

The reason for asking is to understand if there is enough flow to trigger a positive head pump or not and it seems there is. Most require at least 2L/Min to trigger the flow switch. Therefore a universal may not be needed & a positive head pump could be ok.

My test would be to remove the pump and bridge the gap temporarily, do the outlets all flow at least 2L/min hw, if so then that's the tab test for a positive pump.

 

[Tykey]

Great, thanks. I'll give that a go and test the flow rate and see how it is.

 

[Madrab]

Apologies, brain fart - With the monsoons, the trigger value is 0.6L/Min but you're really looking for around 1L/min to avoid any issues.

 

[Tykey]

I've just tested them, and all outlets are at least 1.5L/m so hopefully that's fine.

In looking at a quick comparisson of the pump prices, I notice that the ST Single Monsoon 3bar is only £6 more than the 2bar. Will 3bar (or indeed 4.5bar) give a bit more "oomph" or is that just over-kill and I'll empty the tank in a 5 min shower?!

 

[Madrab]

It's all down to what you want or expect. Yes a stronger pump will move your tanked water faster and give you better overall performance when using multiple outlets at the same time, you will also have a much stronger shower but to be honest anything over 3 bar will feel like it's stripping the skin off your back.

How long it will take to empty really depends on the size of the storage.

 

[Tykey]

Thanks for the advice. I think considering the price difference isn't all that much I'll go with the middle option and look at the 3bar one.