Shower Mixer not pulling hot water

[Goose0211]

We have a standard bar mixer for the shower, recently installed (6 months)
Due to having a gravity fed hot water cylinder in a bungalow we have a hot water pump which works well, however...
The shower really struggles to pull hot water and get the pump to kick in.
The cold water pressure is very good and the plumbers had to reduce that to balance the system.
We have to adjust the mixer temp to nearly max to get the hot water through to the shower and then adjusting afterwards is barely possible without the hot cutting out.
as a side the hot works fine in all other taps.
Any thoughts really welcome as to how this could be fixed or what might be causing this.

 

[ShaunCorbs]

wrong type of shower pump installed bet its a positive head pump needs to be a universal/negative pressure one

the bar mixer has too much resistance on low hot water settings eg 30dc so the hot water isnt flowing enough to active the shower pump

 

[SimonG]

Mains cold water, should really have used tanked cold and twin pump.

 

[Goose0211]

Thanks both,
The pump is a monsoon standard....positive I believe. Not being a plumber I don’t fully understand the difference between positive and negative and why one would be used over the other - I assume with my setup, cold water storage feeding the hot water tank at ground level they would have installed what they saw as the best option?
All cold water taps run off the mains - there is no cold water storage for the taps.

you mentioned too much resistance, can this be altered easily. Getting an expert in at the moment isn’t really an option!

would all bar mixers be the same, ie changing it out would or wouldn’t make a difference?

 

[Mrb]

As said above, you need to take the cold shower feed from the storage tank also.
You will also need to pump this so you have equal pressure hot and cold, so possibly a new pump.
Also worth checking storage tank in loft, you will need to have a minimum of 50 gallons and there’s a chance that if you have mains at cold outlets your tank will be 25 gallon.