New whole house pump - now temperature fluctuating.

[grommett]

Can anyone help with this problem?

I have recently replaced a Salamander 2.5 bar, negative head, whole-house, twin impeller pump with a new 3.0 bar Grundfos pump (Amazon STN-3.0B). It was pretty much a like for like replacement apart from a little alteration to pipework to allow for the pump being a little taller, and having to install sperate full bore isolation valves.

Since installing this new pump, I am now experiencing temperature fluctuations (shower gets very hot if someone flushes a toilet) this never happened with the old pump (replaced because it was leaking and generally unreliable). The pressure seems OK but no more powerful than the old 2.5b pump.

The pump is fed directly from the cold storage tank via 28mm reducing to 22mm near the pump, and 22 mm from the 210 ltr cylinder via Essex flange, no other draw on the pipework before the pump. The pump is on the floor next to the cylinder. Temp stat set to 50c. 100 gallon storage tank in loft. One ensuite has negative head. All shower mixers etc are less than 2 years old and only ever used with softened water. The main shower (the one that I have noticed the problem with) is a Grohe. Pipework from pump to each bathroom is 22mm, reducing to 15mm for each tap/toilet etc.

Let me know if I have left anything out!

Thanks in advance for your help.

Grommett

 

[petertheplumber12]

Sounds to me as if there is a cold water linked to new pumps cold feed, somewhere, It may not have been there before but is now or maybe it was there already but the old pump had non return valves or something that stopped it it from showing up before.

 

[grommett]

Thanks for the reply petertheplumber12. I am not quite sure what you mean. Do you mean there is a draw off the cold supply between the storage tank and the pump?

 

[steve32]

Have you tried the other showers and see if it apply's to them as well.

Is the grundfos pump a whole house pump, I was not aware that grundfos made a whole house pump, the pump you seem to have fitted is only for one shower not a whole house or feeding more than one outlet at the same time.
The grundfos is a positive head shower pump.

http://www.showerdoc.com/3-0-bar-po...-positive-heavy-duty-regenerative-shower-pump

The Salamander was a negative head whole house pump.

 

[dcawkwell]

As before I think you are using a pump not intented as a whole house pump.
You are exceeding the pumps capacity and this cause uneven delivery
of hot and cold. I bet it works perfectly if just supplying the shower and nothing else.

 

[grommett]

Hi Steve 32, the pump in your link is not the pump I have fitted. This is the correct one: http://www.showerdoc.com/grundfos-watermill-amazon-3-0-bar-negative-twin-shower-pump-stn-3-0-b

It is a whole house, negative head pump rated for 52 litres per minute! The old one was only 20 litres per minute.

Cheers


Grommett

 

[dcawkwell]

grundfos only ever talk about showers for this pump.

The selection table gives the amazon extra range as a whole house pump.