We have had an extension built with several new radiators and we also put in a new boiler. We have subsequently had problems and have now been told the heating system in the original part of the house is single pipe while what has been installed in the new extension is dual pipe and this is part of what is causing the problem (poor flow to parts of the existing house). The installer is saying they did not know the existing house was single pipe. I would have thought this would have been fairly obvious or they should at least have checked? Also, it appears they did not adequately flush the system before installation of the new boiler which is now suffering from sludge/blockage. Any help or advice would be most appreciated!
Bascially they've balls it up, and the boiler warranty may be void as they have not flushed the system or added inhibitor. I would take it up with them, they should by rights give you something towards the remedial work (or offer a huge discount if they do the work, if you trust them to work for you again).
I would recommend changing all to a two-pipe system, more work and money but a much better setup. This means taking 2 x 22mm pipes from the boiler (flow and return). Then you need to decide on pipe size, probably best to stick with what they've used in the extension as you need to stick to one size and it seems pointless ripping out new pipework.
So you'll have one flow and one return to each radiator, either 15mm tee'd into the 22mm or manifolds using 10mm pipe. Don't try to feed more than one radiator off each branch, tee into the 22mm for every radiator.
As the new pipework and new radiators will be pretty clear there'll be less resistance, this will be why you are having problems with it starving the existing radiators.
They should have been able to tell how the system was setup - as they have had to tee into the same pipe twice to get the new radiators to work, the radiators that are connected between the 2 new tee's (connections) will be the one's you have problems with, the existing radiators before the new connections should still work.
Thanks htg engineer! Can you say more about how they should have been able to tell if it was a one pipe system? They are saying they could not tell as all they saw coming to and from the boiler was the flow and return pipes. They removed the boiler, put in a new one in a new position (along with a pressurised water system) and connected back up the existing radiators and the new ones in the new extention. Not sure they had to tee the new radiators off the existing flow. So should it have been possible to tell it was a one-pipe system or would it have been difficult? If they had done a power flush, woudl that have given any indication? Thanks!
It is quite hard to say and say who/what is to blame without seeing the job. Basically a single pipe system is as it says, single pipe.
Where did they connect the new radiators to ? they would have to tee into the flow and returns somewhere, so if they lifted the floorboards for the system to be working they would have to have tee'd into the same (single pipe) twice, if you find the two tee's together then they knew what they were doing, if they have tee'd in at different points in the house, they would have to check which was the flow and return, how did they know the pipe they tee'd into was the central heating ? the flow ? the return ?.