New pump, repair pump, wrong pump ?

[Niixsy]

Hi everyone - a bit of a saga here so please bear with me (and sorry about the layman's terminology!).

We have a normal vented configuration with 2 x 10 year old Stuart Turner 1.5bar positives pumping the whole house directly from cold tank in the loft and HWC on the 1st floor. Our main shower is a Grohe 2000 auto of the same vintage. Recently the hot pump has been playing up - sometimes not activating at all. Showers are possible but sometimes with fluctuating presure depending on how the hot pump feels.
I contacted Stuart Turner who suggested that I should be using negative head pumps as the 2 positives might be fighting with each other - but we had no problems for 10 years. Negatives are considerably more expensive on my budget. So my questions are:

1. Is it worth repairing/servicing the pumps - is there anything I could do to verify/resolve the intermittent problem with the hot pump? Is servicing even worth the hassle?
2. Should I replace the hot pump with a simple like for like replacement and ignore the "fighting" issue?
3. Should I replace both pumps with negative heads and is there any guarantee that this would solve the potential "fighting" problem?

I would really like some confirmation about the science behind the pumps fighting to convince me that the negative pumps will really do the trick for the money.

Thanks for listening !

 

[paulusgg]

The use of either positive or negative pump is dependent on the position of the elements in relation to each other. Where is the pump situated? Is the shower head higher than the cold water storage tank? And almost all shower valves require a balanced supply to function properly so if one pump is failing the supply wouldn't be balanced.

 

[Niixsy]

Hi Paulusgg - the cold pump is in the loft adjacent to the cold water tank and the hot pump is on the floor next to the HWC - so a floor apart - the HWC is lowest. The main shower is on the ground floor - i.e. below the HW pump. I would think the length of pipe to the shower is shorter for hot than cold if this makes a difference.