Cleaning out Central Heating - any tips I should bear in mind?

The_Governor

I've got an open vented system, I've got some Fernox F3 and will be adding the Fernox Inhibitor after cleaning.

The system is 10 years old (just) works fine, expect for some glugging between the h/w tank and the boiler, but it's done that since we bought the house 8 years ago and never seemed to effect the performance of the system.

One rad upstairs needs regular bleeding, I'm hoping cleaning/inhibiting will solve this (unless it's a design problem of course).

I have some queries and hope someone who's done it before can just give me bit of guidance.

On the cleaner it says flush the cleaner out at all drain points - all the downstairs rads (8 of them) have drainpoints, so that's not too bad I can stick a hose on each.

The boiler also has a drain point above it, do I really need to drain from that as well, as it's fairly hard to get to?

When I run the cleaner through, as well as firing up the heating, should I fire up the hot water too so the cleaner goes around the hot water tank as well?

In general, how likely is it the cleaner will expose leaks sealed by corrosion?

Once the cleaner is done, I was planning to drain from one rad for the most part, leave the F&E tank to keep refilling to get a flow of water through, then do a final drain from each of the other rads. This is mostly to avoid totally draining the system dry and risking airlocks...

Would appreciate any tips or gotchas from the more experienced DIYers

The_Governor

Up for anyone who missed it

jimmo

Sorry to see you’re not getting any responses yet.
It’s got to be 30 years since I used Fernox. That was when I lived in a hard water area.
As far as I recall, it is very important to ensure that you give the system a really good flushing after the “treatment”. In those days the instructions were to run the heating full blast for 24 hours for the “treatment” and, yes, put the hot water on.
When I did mine I only drained the system from the lowest drain point. I also flushed the system twice.
Points to bear in mind,
1) You obviously have to, at least partially, drain the system to make sure the cleaner actually gets into the system. It won’t do any good if it stays in the header tank.
2) The water that you initially drain off will be absolutely filthy. Be very careful.
3) After the “treatment” the water you drain off will be even worse.
4) It takes an awfully long time for the system to drain if you leave it to its own resources. I used a Black and Decker water pump accessory in my drill to encourage it. I also had the wife posted upstairs and as soon as she reported that the radiators were bubbling we opened the bleed valves on the radiators to allow air in on top of the water.
5) There is every danger that cleaning the system will uncover hidden leaks. You do need to be prepared. We had one such leak and fixed it “instantly” with a form of instant sealer which came in 2 parts. Mix them together and slap it on. I assume they still sell it.
I don’t think your idea on partially draining the system after cleaning is a good idea. It is apparently most important to clear the cleaner from the system before adding the inhibitor.
I drained our system dry, filled it up with cold water and drained it dry again. Then I actually flushed it. Switch on the water but leave the bottom drain point open until clear water comes out.
Then add the inhibitor.
That worked for me and I didn’t have any problems with airlocks.
Please remember, I am just a bodger and definitely no expert.

It really is a messy job.

The_Governor

Thanks jimmo - any and all tips accepted no matter how old they are

latecomer

One thing to be careful of is the water that is drained out will probably be black, dont get this on your carpets of anything else good as it makes a real mess.

I'd definitely fire up the hot water as its all part of the same system and you want to clean out as much muck as you can.