Thermostatic Shower Issue

Hi,
I have just installed a new thermostatic shower valve (Screwfix - Moretti) and connected it with new 15 mm pipe work (around 5m to the boiler) back to my 18 month old potterton combination boiler. Upon testing the shower I found it runs from cold to luke warm even with the temperature knob as high as it goes (there is no other temperature control).
The hot pipe is very warm and I have left the shower running for a couple of minutes with no difference, even when hot water arrives at the taps in 10-15 seconds and as I said the pipes get very warm.
When fitting the therom control it suggested adding the supplied flow restrictor (plastic) valves if the pressure was greater than 0.5 bar, my system is so I fitted them.
When turning off the cold supply completly the shower runs very hot, with the cold open a 1/4 of the way it is warmer but not as warm as I think it should be. I also removed the flow restrictor from the hot supply and think this made a little difference (i.e. it was a little warmer).
The hot supply seems to have a lower pressure than the cold and I am not sure if that is the problem and if there is anything that can be done.
Basically I am out of ideas, I am not sure if it is an issue with differing pressures, a faulty theromstatic valve or something else.
Any advice is greatly appreciated.
If you need and more info please let me know.
Cheers,
James
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Are you 100% certain you have the hot and cold the right way round?
Mike
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yes I checked that 3 or 4 times before fitting and 3 or 4 more once I realised it was not working as expected :-)
Also according to the manual, getting them the worng way round would result in either hot or cold rather than what I have which is cold to luke warm.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.