New combi,problem with rads !! urgent help needed! All aspects of plumbing questions and answers, help, tips and information

[misery]

Hi guys ,
Had a new combi boiler fitted yesterday,I ran all the new pipework (except Htg flow and return) and gas connection ,corgi guy came to commision and do final connections.
He diconnected flow and return pipes from old boiler (baxi solo 50/4rs) and connected onto new system (Heatline c28)
The problem I have now is the 4 rads upstairs are only a little more than warm and the 4 downstairs rads are stone cold except a new one fitted in the same room as the combi which is about as warm as upstairs ones.
I rang the engineer who said prob got the flow and return wrong way round,this baffles me slightly because on the rads that are warm when you touch the tails the side of the trv is very hot and the lockshield valve warmish,all tails dowmstairs by the way are stone cold,the flow and return pipes leaving the boiler are very hot and hot.I thouroughly flushed the system out last week and have bled every rad numerous times ,
every rad on the old system was working ok,so I assume this rules out balancing.
I have a plasterer coming early next week ,dont want to put him off have waited ages for him already so any help asap would be greatly appreciated.
Many thanks
Misery.

[plumbbob]

the obvious option is there is still loads of air trapped in the system causing a reduced flow. Need to remove a radiator valve or bleed valve and feed into a bucket. The rapid flow should blast air out of the system.

[misery]

Hi Plumbob,
Tried what you suggested,still no joy.
I actually took off two big rads in dining room and lounge ,they were full of sludge ,even after flushing and draining down 3 times ! Have left them off completely ,have some new ones to replace them with at a later date.
The only other rad left downstairs is in the hall which I also took off and noticed was full of sludge,took into garden and blasted through with hose jet for half an hour and replaced. Re filled system bled all rads and hey presto,same problem,upstairs fairly warm ,downstairs nothing.
Is it possible that flow and return pipes on installation got mixed up,even if the tails with the trv's are hottest?
Look forward to your response,
Many thanks,
Misery

[plumbbob]

Fundamentally, there is no difference between a flow and a return as far as pipework is concerned. What makes the difference is the on/off valve should, from a textbook point of view, be in the flow, and the lockshield in the return. Many older TRv's were directional so had to installed in the flow unless they were adjustable. If reversed, they still worked, but would often make a noise.

To me it sounds as if your system could be blocked with sludge. When a new boiler (particularly a condensing boiler with a fragile heat exchanger), is installed it is essential to thoroughly flush the system to remove all debris that may cause future problems.

Connect the hose to one of the radiator pipes and another to the opposite pipe and flush the heating circuit extensively. When you have removed all the slurry, replace the rads, and refill, filling the downstairs rads first then the upstairs.

If you still have a problem you can be pretty sure it is trapped air. Air can be a devil to remove sometimes and it is just a question of being persistent.

[misery]

Hi Plumbob,
Thanks for the reply,did in fact change the flow and return pipes today and still the same, so frustrating!!
I take on board what you say about sludge,trouble is everything was working fine with the old boiler,sludge or not,but as you say new boilers probably more sensitive.
Just to be clear,are you saying drain down everything,remove all rads,close all valves except one pair on flow and return take the valves off and attach a hosepipe to each of them and give a good flush through,would this be better on an upstairs or downstairs rad??
Many thanks for your help so far.
Misery.