Sorry to cross-post from the Home DIY thread but looking for urgent advise.
We have a vented heating system with cold water tank and hot overflow in the loft. The hot water overflow in our loft is overflowing (through the exterior pipe) and the boiler periodically overheats. Plumber says there is a partial blockage and that we need a powerflush.
I have heard much skepticism about this procedure, from it usually being unnecessary to it causing leaks in older pipework. I suggested to the plumber that we might try a chemical clean first but he says this will just pour out of the overflow due to the blockage.
Is there anything we should try before we do this powerflush? Can the chemical be introduced in such a way that it stays in the system for longer before reaching the overflow?
Should add that we are going to be changing almost all the upstairs rads soon so it strikes me we should do this before anything else.