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If they are virtually new i doubt the build up of sludge is a problem in the infancy of a system, but it is worth checking the level of inhibitor installed anyway. The problem more than likley is due to poor installation methods, mainley the commisioning side of the installation. If the rads have not been individually ballanced properly then it is possible that the flow is too excessive and does not have time to circulate round the rads before leaving via the return. So i would check each rad for correct ballance first to see if this cures your problem. Best way to check is to take off the tamper proof cap off the return side of the rad valve and with a suitable tool ( small adjustable or grips / pliers ) and turn it anti clockwise. If it will only turn by a small amount say less than one full rotation or even not at all then it has not been balanced and is fully open, allowing the full flow through all at once and resulting in wasted energy and poor ciculation as you describe. If you find this to be true and need to know how to ballance a system then post again. Good luck Gasman.
OK with the heating on full and running for say 1/2 an hour so it should be up to full steam so to speak. Start on your first rad by turning its control valve up to max on the flow side this is the valve that you can turn and probably has numbers on it 5 or max is fully on, or if no indication of which is on then it should be turned fully anti clockwise till it wont go anymore. Then pull off the tamper cap on the remaining valve ( this is called a LOCKSHIELD valve ). Turn it fully clockwise till it is in the off position as posted earlier you will need a tool for this. Once you are happy that it is in the off position then turn it just by half a turn anticlockwise and leave it for a couple of mins and see if the whole rad heats up properly. if not try another half turn and repeat untill the desired effect. Do this on every rad. once set they should never be touched again and the tamper proof cap clicked back into positio. The method i have just described is a bit of guess work and not that accurate but it will work. You will find that the rads closest to the boiler will only need to be opened by a small amount compared to the rads furthest away from the boiler that will need to be set by maybe a couple or more. We actualy use pipe thermomitors to set them a. There should be a difference of 10 degrees C between the flow side and the return side of the rad. And also double check that there is no air left in them by bleeding each rad. Any way Good luck missieb.
If you have TRVs (Thermostaic Radiator Valves ) fitted, then turn the knurled collar of the valve ( just under the plastic section of the valve head ) anti clockwise to take the thermostatic head off the valve body. Do this first so that it cannot shut down the rad and spoil your hard work. You will find a small rod/pin type piston that will be sticking up and not stuck down, if it is give it a tap or move it up and down with your pliers till it moves freely but do not pull it all the way out, or you will get wet and the water is going to be very hot !!! When You have balanced the rad and fitting the TRV head again just sit it in position and make sure it is in the max or number 5 position then push it down and locate it by just giving it a twist left and right, you will feel it drop into position then screw the knurled collar back onto the valve body and set it at number 3 then all should be OK again. Best of luck again Gasman.
Well Gasman your answers are outstanding. I have printed the whole sequence off & will keep for future reference. Currently I have 2 radiators disconnected while a room is being replastered so I may need to do the exercise again when they go back on. But now I know the cause and the solution. Many Many Thanks. missieb
Hi just came across this post, its fantastic and so well explained. I have one question however about the TRV,s, we replaced ours using bi way TRV's so after checking the heating during warming up, some of the TRV's are on the return run. Do I still close down the locks hield valve in the same way even though its on the flow side. Cheers and thanks again