Right... I've spent most of today, draining, flushing (repeat twice) our CH system and also removed and hose-flushed three problem rads (they're all cold, basically). I've also added Fernox F3 and will leave it to circulate now for a couple of days, as per the instructions.
However, the three rads that I flushed remain resolutely cold, despite having removed rather a lot of black sludge/oxide from the hose-out. Indeed, the rads themselves were allowing clear water to flow free before I put them back on the walls, so I'm pretty sure the rads themselves are now fine. So I would expect at least *some* warmth in them. All other rads are now wonderfully hot.
As a result, I fear that the pipework between the troublesome three must be blocked - and I'm doubtful whether Fernox F3 will be able to penetrate. For reference, the three rads are all in sequence (well, so far as I can tell) and are all on the ground floor. The pipework between the rads is small bore (half-inch/12.5mm).
So, where do I go from here? Is powerflushng the way forward? Or (forgive my naivety) is there some way to physically brush out the pipes, using the pro equivalent of a pipe cleaner? Or does anyone have any other ideas/suggestions?
Note, too, that the boiler seems to overheat and lock-out after about 30 mins. My theory is that this is because this is the time it takes to heat the first 11 rads (the 3 troublesome ones are at the end of the sequence) before the backed-up water boils in the pipes (I can literally hear that before the boiler locks out). Or is this a bonkers theory?
Of the three rads, one has a TRV that seems to be functioning (ie, the pin moves under resistance, as I would expect) while the other two are simple manual valves. I can feel the heat-feed pipe is hot into the first rad but cold on the exit (and then on to the remaining two).
All advice appreciated, as ever.
Harry.
However, the three rads that I flushed remain resolutely cold, despite having removed rather a lot of black sludge/oxide from the hose-out. Indeed, the rads themselves were allowing clear water to flow free before I put them back on the walls, so I'm pretty sure the rads themselves are now fine. So I would expect at least *some* warmth in them. All other rads are now wonderfully hot.
As a result, I fear that the pipework between the troublesome three must be blocked - and I'm doubtful whether Fernox F3 will be able to penetrate. For reference, the three rads are all in sequence (well, so far as I can tell) and are all on the ground floor. The pipework between the rads is small bore (half-inch/12.5mm).
So, where do I go from here? Is powerflushng the way forward? Or (forgive my naivety) is there some way to physically brush out the pipes, using the pro equivalent of a pipe cleaner? Or does anyone have any other ideas/suggestions?
Note, too, that the boiler seems to overheat and lock-out after about 30 mins. My theory is that this is because this is the time it takes to heat the first 11 rads (the 3 troublesome ones are at the end of the sequence) before the backed-up water boils in the pipes (I can literally hear that before the boiler locks out). Or is this a bonkers theory?
Of the three rads, one has a TRV that seems to be functioning (ie, the pin moves under resistance, as I would expect) while the other two are simple manual valves. I can feel the heat-feed pipe is hot into the first rad but cold on the exit (and then on to the remaining two).
All advice appreciated, as ever.
Harry.