Radiator variable heat

10 year old system , no problems to date, sometimes have to bleed the ocassional cool radiator.
Recently added a conservatory and fed off an existing upstairs bedroom radiator down into conservatory and onto new supposed high output radiator.Fitting finished last weekend and then turned back on HW & CH ... took a few hours for all rads to heat up ....noticeably the new conservatory one took the longest.First evening it seemed hot, since then it has cooled down and now feels very lukewarm.
The 10mm plastic microbore pipes which were run off upstairs bedroom to the new rad ...... when you feel them , one feels fairly hot ... the other very cool.
I bled just after the fitting.
Seems to be no air in the conservatory rad today.
Any ideas ?

"fed off an existing upstairs bedroom radiator"

If it is a 'high output' rad, you really should run a new length of pipe rather than tee off an existing radiator feed.

Either way, regarding cold rads, have you forgot to open a valve somewhere, or perhaps let air get into the pump, or perhaps an airlock somwhere. Or pehaps a blockage somewhere in the pipe.

Hi

I believe a new pipe has been run correctly (I would attache a image if I knew how).
All existing rads are open and extremely hot to touch, only this new one seems luke warm.
All existing rads have both feed and return pipes at one side and are hot to touch.The new rad has these at either end and only one end is hot to touch the other is much cooler including the pipes attached to it ...........could this be something ? Similarly feeling the heat of the pipe upstairs one feels much warmer than the other ?
Can you connect the feed/return in the wrong order and how would this effect the rad ?
Is the valve on the left side of rad (which is not the one which you can screw back and forth) got any impact ......... could it be somehow causing this ?
Could it be balancing thats needed ?

"Could it be balancing thats needed ?"

I'd not considered that this could be the problem, sorry....

Anyway, to 'balance' the rad, take the cover off the valve that cannot be turned by hand, and then open the valve a bit more (use a spanner), and see if this solves the problem.


The other issues you have questioned are probably not the cause...

Are the pipes to the upstairs radiator that U tee'd off also 10mm microbore? If they are then they may not be able to supply enough heat to both radiators. Try turning off the bedroom radiator to see if the new rad heats up any better.