De-scaling a thermal store with DS-3

[barrycrook]

Hi All,

I have a thermal store which provides combined hot water and central heating. It's been rumbling recently and after some research it appears it requires de-scaling.

I have tried X400 followed with X200 + X100, but that fixed it for a short period. But i read on the forums that X200 is only a temp solution and DS-3 gives better results.

Looking at the Fernox DS-3 instructions these are just for hot water systems. I'm thinking of turning off all the radiators first and keeping the central heating set to off. Drain the tank/boiler and fill with DS-3 and fill back up. Set the stat to 60 degrees and set the hot water on.

This should just de-scale the tank and boiler. But when draining/rinsing the system, do i need to just drain off the boiler/tank or the complete system? I have 3 drain points: boiler, tank and rads.

Would any DS-3 get into the heating system if it not turned on?

Thanks

Barry

 

[45yearsagasman]

What thermal store is it and what part are you trying to descale?

 

[barrycrook]

There is no mark / name on the tank, i'm trying to de-scale inside the actual tank. not inside the hot water coil. i think there is a lot of build up in the base as the drain valve is clogged up.

 

[Agile]

I think it would be very unwise to use DS3 to descale the tank.

Are you sure its full of something rather than the drain cock washer stuck?

Tony

 

[barrycrook]

The tank rumbles every now and again, which i believe indicates localised boiling, which is linked with scale. Would you still recommend DS3?

 

[ChrisR]

WHat sort of thermal store is it?
Is it heated directly from the boiler, or indirectly via a primary coil?

DS-3 is to dissolve limescale, not magnetite/boiler scale. Nothing you've put in so far will do a lot to dissolve limescale. X400 is pretty timid on boiler scale too.
DS-40 will attack boiler AND lime scale, as will Kamco FX-2.

There will be a pump to CH circulation but unless there's a 2 port you'd get some thermal convection circulating it through an "off" pump. If you use an acid for scale(s) you'll have to use a neutraliser, which does no harm, so you'd "do" the whole system.

Work out the volume of the thermal store. You'll need a lot of chemicals whatever you use.

 

[barrycrook]

Hi ChrisR,

Yes, it is directly heated from the boiler, the same water is then used to pump around the CH. A coil in the tank is used for HW. So the tank temp is required to be quite high 70-80 degrees.

I don't think it has been regularly maintained and obviously the high temp will cause the scale inside the tank. I know the X200 is some sort of de-scaler but i think it is for mild issues. This has helped but not solved the issue.

I estimate the tank to hold around 980 litres of water.

What would be the best steps with DS-40 or Kamco FX-2?

As this system is around 20 years old are acid based solutions advisable?