Boilermate iii radiators downstairs not working

Hi A long one but I though I would try and give as much info as possible for anyone who is able to provide some help if you can.

I have a boilermate 3 upstairs and potterton suprima 70 boiler downstairs. The hot water is fine and I have no problems. I do have problems with the radiators particularly downstairs; these are cold. The one next to the potterton may be hot or warm. I have had British Gas out 4 times so far all giving different reasons for the problem.
BG engineer 1: Said valve was stuck so he freed it up and said that should solve problem (Not sure if he meant diverter valve though it is the one with a moving arm/lever on it)
BG engineers 2:Thermostatic valves on radiators stuck so he banged them and freed pins. This helped for a couple of days
BG engineer 3:balanced radiators. This helped for a few days
BG engineer 4: Did nothing but said these systems are renound for sludge build up. I though he was leading toward getting me to have a powerflush from BG so I was waiting for the £700 question... but No. He said the the manufacturer of the system does not recommend it so BG will not do a powerflush of the boilermate 3. He said the only way is to actually take out the boilermate 3 tank and tip it upside down to empty the sludge out but BG do not cover this under the homecare agreement. I would have hoped that Britich Gas would have mentioned this to me if there was an issue with these systems.

I asked him if the pump could be at fault (Not the one going to the heat exchanger - the other one!) (It gets hot and sound like it is vibrating ok) He said he could try and is due to replace this in the week. He checked one of the radiators to see if there was sludge coming out of the hallway one . The water was black and free flowing as you would expect but not exactly sludge. The pipes going to all the radiators are 8mm I think so this may not help but would this cause a blockage with sludge if sludge was an issue? The upstairs rads get quite hot though the bathroom radiators upstairs are warm to cold. It is a 5 bed house with three bathrooms so we have 7 radiators upstairs + 3 bathrooms towel radiators and 8 radiators downstairs.

The pins on most of the radiator thermostaic valves seem OK though when I banged the valve in the bedroom upstairs and move the pin it releases some hot water through the radiator so it looks like this one has a tendancy to get stuck. I have left this permanently on at the moment.

So far BG have not replaced parts or valves. Do British Gas have an unwiritten rule to do what they can in labour ie freeing and banging valves so they do not need to supply parts? They seem reluctant to change any parts not that I am an expert!!!

One other thing there is a red light flashing (looks like number 14) on the boilermate 3 diagnostic panel . I can just see it through the holes in the side!

Many thanks

Chris

Sludge is a problem
Because not enough inhibitor is not put in when installed.
You could try having sludge remover applied to system
And then later a drain down and manual flush.
CAN not power flush the unit.
Can take heater or blank out to see if sludged up.
Tipping up side is a bit drastic!
Have you the book on the unit?
If not down load 1 from Gledhill.
Also if you require an engineer try asking Gledhill or
Look on
http://www.segel.co.uk/
To see if there is one in your area.