Cold Expansion Bottle??

[akymark]

i own a 53 mondeo 115 tdci. the other day the heater wasnt as hot as it should be so i checked the water level and it was low. topped it up but the temp guage wasnt going to the middle as normal only to about a quarter,since then its had a new stat and a new pump but still the gauge isnt where is should be and also when i check under the bonnet the expansion bottle is clock cold, ive bleed the pump and even opened it with engine on just so i know the pump is pumping which is it. so my question/problem is........should the expansion bottle get warm by having a constant flow through the small pipe to it or is it normal for it to remain cold..ps the heater is lovely and warm but im still not happy with gauge as it seems to take ages to get to the middle if at all and it keeps fluctuationing between the middle and a quarter.....