Leaving Fernox F5 in system

[chrisw99]

Hi all,
First post here so go easy on me.

I've got British Gas homecare and just had them out for a boiler problem as it kept overheating, he diagnosed a blockage in the gravity flow pipes so all the heat was kept down at the boiler end. To cut a long story short he advised a powerflush (for £600-700) or a new boiler as this is quite old and getting obsolete, but he said it's worth adding some Fernox F5 as this could quite easily clear the blockage, so he added half a litre to a radiator and advised leaving the heating on to flow it around. Fingers crossed this will work and the heat will flow upwards to the cylinder again.

What has concerned me is getting back to work I googled F5 and everywhere I read says it should be cleared out once it's done its job, but he told me its perfectly safe to just leave it in.

Just wondering what the advice here is?

 

[Harvest Fields]

Power flushing chemicals are not designed to be in the system long term. If the blockage is removed it should be flushed out ASAP.

 

[aggis]

Different chemicals can be left in the system for different length of time, it's always best contacting the chemical manufacturers. In your case Fernox, they will happily tell you what they recommend.
After that it's down to your experience & risk, as there can be other factors. I'd stick with their advice.
But with it being gravity pipework to the cylinder, it's going to be an old boiler & system, I'd get more advise form other engineers as you could be spending a lot of money & not improving things, or just temporarily improving & being back to square one.
£600-700 & maybe still a re-pipe £££'s could go along way to a new boiler with different controls that will instantly start saving you money on running cost.
Get more advise.

 

[ShaunCorbs]

Normally about a month maximum, then needs to be drained and filled and fresh inhibitor

 

[chrisw99]

Different chemicals can be left in the system for different length of time, it's always best contacting the chemical manufacturers. In your case Fernox, they will happily tell you what they recommend.
After that it's down to your experience & risk, as there can be other factors. I'd stick with their advice.
But with it being gravity pipework to the cylinder, it's going to be an old boiler & system, I'd get more advise form other engineers as you could be spending a lot of money & not improving things, or just temporarily improving & being back to square one.
£600-700 & maybe still a re-pipe £££'s could go along way to a new boiler with different controls that will instantly start saving you money on running cost.
Get more advise.

Thanks for that, I've been seriously considering getting a combi boiler soon anyway as this is now my 4th boiler breakdown in 4 years, luckily the parts are still available and fairly cheap (a Halstead Best 50) , but I'm probably wasting £££s in efficiency at the moment.

As a lowly homeowner though, if BG advise me it's safe to leave in I shouldn't really need to question it.

It's a vented system with a feed tank so I can easily run it through till clear and add some inhibitor in a couple of weeks time.

 

[king of pipes]

Time for a upgrade bud dont waste £600 + put it towards another boiler. If not F5 dont leave it in for more than 2 weeks max drain and flush out before refilling and adding new inhibitor. Cheers kop

 

[chrisw99]

Time for a upgrade bud dont waste £600 + put it towards another boiler. If not F5 dont leave it in for more than 2 weeks max drain and flush out before refilling and adding new inhibitor. Cheers kop

Thanks for all the replies.

Am I correct in thinking that if I did fork out for a powerflush, this flushes by pumping around the CH circuit. Would that actually flush the flow and return gravity pipes from the boiler up to the cylinder anyway? If that is where the blockage lies, then a powerflush seems redundant if it's not going to actually flush where the blockage is.

Similarly, adding Fernox F5 or equivalent and running the CH to spread it around, will it actually get into the DHW flow/return pipes from the boiler or just the CH? I guess so but will take a bit of time to just spread through the water.

 

[aggis]

If it was Powerflushed, the engineer would Powerflush the Radiators then isolate the radiator circuit so he'd then just flush the DHW circuit.
Flushing does work but you need the pipe to not be completely blocked.
As said with your old boiler system, probably better investing in a new boiler, a combi might do. But get advise from independent engineers that have looked at your system

 

[chrisw99]

If it was Powerflushed, the engineer would Powerflush the Radiators then isolate the radiator circuit so he'd then just flush the DHW circuit.
Flushing does work but you need the pipe to not be completely blocked.
As said with your old boiler system, probably better investing in a new boiler, a combi might do. But get advise from independent engineers that have looked at your system

Its not a complete blockage in the DHW, it does flow but takes a bit longer than normal, e.g. from cold the hot water cylinder can take a couple of hours to heat rather than the 20-30 mins it used to. The problem is it takes just that little bit too long to get the heat away from the boiler that it causes it to keep cutting out.

I've had a couple of engineers look at it and neither seemed to have experienced an old fashioned gravity fed cylinder before that doesn't have any valves, stats, just pure heat flow up from the boiler. A bit of head scratching then "if you replace with a combi you won't need those pipes that are blocked anymore".

Yes a new boiler would be a good idea one day, but as the boiler is working perfectly, the CH is working perfectly, it seems a bit daft to spend thousands I haven't got when there's probably just a few cm of pipe somewhere in the DHW flow/return that needs clearing or cutting out/replacing. (Yes my tune has changed since earlier when i was getting tempted by a Combi, but I've now spoken to the missus who has reminded me I don't have ££££s to spare...!)

I cleaned out my F&E tank in the loft at weekend in readiness for doing a drain/refill to get the F5 out. Tested the drain cock and got a bucketful out, and the F&E tank filled. So I think before spending dosh, do a few drain/refills to clean out any crud, add some x400 and leave a few weeks, drain again, and see if it's made any difference.

I think it probably will, the F5 has been in a few days, and I'm sure the time it's taking from the pipe out from the boiler getting too hot to touch to travel a couple of metres upwards seems to be decreasing as though the flow is improving.

 

[king of pipes]

Dont go mixing different makes of chemicals bud stick with fernox now you have started using it .cheers kop