Flushed three rads, added Fernox F3, still cold...

[hsabbers]

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.

 

[Boilerman2]

It is unlikely that pipes are blocked -although not impossible,
What actions have you taken, leading up to deciding to flush the system,

for instance have you tried balancing the system? are all the faulty rads at the end of a circuit?? are there Thermostatic Rad Valves with stuck pins??
is the pipe work airlocked?
It seems strange to me that there is no circulation at all!!

 

[croftxxx1]

hi asab
There will be an air lock in the pipe work......start from the nearest rad to the boiler and bleed off about a pint and then move on to the next....you will get water coming out as expected but the air lock will be in the pipework,,,,try to get at least a pint from the cold rads.....if you have motorised valves on the system this may be causing a problem remember to put fernox back in the header as you near finishing the bleeding

 

[hsabbers]

It is unlikely that pipes are blocked -although not impossible,
What actions have you taken, leading up to deciding to flush the system,

for instance have you tried balancing the system? are all the faulty rads at the end of a circuit?? are there Thermostatic Rad Valves with stuck pins??
is the pipe work airlocked?
It seems strange to me that there is no circulation at all!!

Yes, all the rads are at the end of the circuit (so far as I can tell - the pipework is mostly hidden), but they're all in line, one after another - so it makes sense that they're at the end of the circuit.

As for balancing, at the moment I have all valves fully open, to circulate the Fernox. This includes on the dud rads. One rad does has a thermostatic valve but, as above, the pin seems to move up and down fine (I have the control head off the valve and the pin seems fully up, thus open).

 

[hsabbers]

hi asab
There will be an air lock in the pipe work......start from the nearest rad to the boiler and bleed off about a pint and then move on to the next....you will get water coming out as expected but the air lock will be in the pipework,,,,try to get at least a pint from the cold rads.....if you have motorised valves on the system this may be causing a problem remember to put fernox back in the header as you near finishing the bleeding

I will try that - thanks. May sound silly but how best to capture the water coming out of the bleed valve? Obviously I usually use a towel to capture the escaping water but if I have to capture 1 pint of a fast-moving jet, tips appreciated - a deep jug, I suppose?

 

[croftxxx1]

pint jug will do.....................i have flushed many systems through and i often guess how long its going to take for all the rads to be singing again

 

[Boilerman2]

If you have opened ALL of the valves fully as you state, then this is probably why the end of line isn't working - water will always take the easiest route around the system, by opening the valves on the nearest Radiators you have C***ed up the systems "Balance"

 

[SpecialK]

Does the boiler actually overheat and lockout, requiring a reset or time to cool? Or does it just get up to temp and stop heating the circuit? Can you hear the boiler getting very hot?

Could be a pump issue?

To check for a blockage run some water from each of the removed rad valves.

 

[hsabbers]

Does the boiler actually overheat and lockout, requiring a reset or time to cool? Or does it just get up to temp and stop heating the circuit? Can you hear the boiler getting very hot?

Could be a pump issue?

To check for a blockage run some water from each of the removed rad valves.

Yes, it overheats and locks out (goes to red light - needs to be manually reset). This event is preceded by kettling in a pipe in the cylinder cupboard - can't really tell which pipe.

The pump was replaced in summer (by Heateam, not me) as was the diverter valve. The boiler's PCB has also been replaced.

 

[hsabbers]

If you have opened ALL of the valves fully as you state, then this is probably why the end of line isn't working - water will always take the easiest route around the system, by opening the valves on the nearest Radiators you have C***ed up the systems "Balance"

Right. Well, I will try reducing the valves on nearer radiators to get balance. However, would you expect the last three rads to be *completely* cold, as they have been?

Also, a slight update here... the 'middle' of the three rads is now getting hot! (When I say middle, I can't be sure it's in the middle in terms of their plumbing - there's one large rad in the living room, then one small one in the hall to the right, that's now getting hot, then another small one in the downstairs WC that remains completely cold, including at the flow pipe -- the other two problem rads have warm/hot flow pipes).

 

[SpecialK]

Sounds to me like the boiler is not getting enough water through it, or there is air in the circuit.

Is the pump external, can you confirm its spinning?

What kind of boiler do you have? Header tank etc full of water and does it drain of water when you drain a rad?

 

[hsabbers]

Sounds to me like the boiler is not getting enough water through it, or there is air in the circuit.

Is the pump external, can you confirm its spinning?

What kind of boiler do you have? Header tank etc full of water and does it drain of water when you drain a rad?

It's an external Grundfos and it's only three months old. Sure sounds and feels like it's spinning but not sure how to tell otherwise. The boiler is the dreaded Potterton Suprima 50. The header tank has water and seems to work as expected - I've drained the system twice today and cleaned out the header tank, to get rid of oxide etc.

 

[hsabbers]

Is the pump external, can you confirm its spinning?

I just checked, specifically a Grundfos UPS 15-60 (like this: http://bit.ly/tugkVg). As I said, it's essentially brand new and sounds like it's spinning.

 

[SpecialK]

If its easy enough to do then remove the pump and check to see if the impeller is spinning and free of grime. Don't run the pump dry for any length of time.

Is it possible you have an airlock? Did you open all automatic valves when draining/filling? Does the boiler have a place to bleed air...

 

[hsabbers]

If its easy enough to do then remove the pump and check to see if the impeller is spinning and free of grime. Don't run the pump dry for any length of time.

Is it possible you have an airlock? Did you open all automatic valves when draining/filling? Does the boiler have a place to bleed air...

Not sure I'm confident enough to remove the pump, tbh. Again, it is virtually new, so I have little reason to doubt that it's turning -- and it sounds and feels like it is.

Yes, I can open all valves (in TRVs) when filling/draining -- though draining has been slowish downstairs, and I resorted to the drain-off valves to get it done (all downstairs rads have drain-off valves, conveniently).

I have no idea how to bleed air from the boiler/system, other than via the rad bleed valves.