Fernox / Sentinel

[John]

I have just removed a radiator for decorating and recently had a partial drain down to replace a 3 way valve. I am now wondering what to add into the system. I have used Fernox and Sentinel X100 in the past. I guess the system is now a bit deficient of additives. System:

Worcester Heatslave Highflow Combi

11 radiators

Each fed by single end flow / return valves

System fitted 1988 (probably the last house to use the dual Yorkshire valve!)

Pipe 6mm microbore

The system seems to be working well.

I would like an additive that will dissolve any sludge and keep it in suspension. I don't really want to clean / drain / flush as this adds lime into the boiler. I intend to add whatever is recommended into the radiator that I will be refitting before I open the valves.

Any suggestions / recommendations?

[Andy Hall]

If it's all working OK and the water is reasonably clean - i.e. a straw colour from the inhibitor; then I would be inclined to add more if it's due and leave alone.

If you want to add something via the radiator, there are gel versions of Fernox in a tube that can be injected through the vent. With an empty radiator you can do this a little at a time, stopping to let the air out. Then close the vent and open the valves. Vent as normal.

There are flushing agents by both of these manufacturers, but you need to really flush the system and add the material and run hot for a few days. Then you drain and flush and finally refill with fresh inhibitor.

I wouldn't worry about the impact of flushing on the boiler. Each time you fill you are talking about the scale from maybe 100 litres of water. Unlike a HW cylinder where several times this amount per day may be going through, this is not going to have any noticeable impact on the heat exchanger.

.andy

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[Christian McArdle]

Don't worry about hard water. As the water is not continuously replaced there is only a finite (and small) amount of calcium in the water. The water softens very quickly as a undetectable layer of limescale forms around the system. You only really get limescale on the primary side if you keep topping up (manually or automatically, depending on the system) which introduces new calcium over time.

Flushing the system would be a very good idea.

Christian.

[Christian McArdle]

I'd replace every three years.

Christian.