Descaling hot water cylinder & pipes with Fernox DS3

ed110220

Hi all,

the other week the hot water tap in our kitchen suddenly only gave a trickle of water. The hot water in the bathroom immediately above works fine, so my guess was a blockage of the pipe between the two.

I was recommended to use some Fernox DS3 descaler in the the system as it seemed it was probably some limescale flakes blocking the pipe. The pipe between upstairs and downstairs will most likely be original to the house and about 65 years old.

So I tied up the ballcock in the header tank, ran the hot water taps till all the water came out. Then I added the DS3 predissolved in hot water as per the instructions (nothing about quantity to add though, so I added about 500g). Then refilled the header tank to just cover the inlet.

Then started up the boiler to heat the water. Went to run the hot water till it ran orange and it just ran and ran clear... realised the hot water outlet is at the top of the cylinder and the inlet is at the bottom so there was a full cylinder of fresh (non descaler) water. So I added more water to the header tank, more descaler, ran the taps again till it came out orange.

Now I've been letting a little water out every 15 minutes or so but if anything the flow is worse!

Will it take more than 2 kg of Fernox to descale the system? The hot water cylinder is of an unknown age, but I would guess perhaps 30 years old.

Any other ideas?

plumb1_2

I would say you have a faulty tap, or air-lock if your bath tap is ok

ed110220

plumb1 wrote: »

I would say you have a faulty tap, or air-lock if your bath tap is ok

Thanks. That's a bit of a pain if the tap is faulty as it's only been replaced within the past year. Is there a DIY solution to an air lock?

The pipework is in the wall, so inaccessible without ripping the plasterboard off.

The water came out full of tiny rust-brown flakes.

malc_b

ed110220 wrote: »

Thanks. That's a bit of a pain if the tap is faulty as it's only been replaced within the past year. Is there a DIY solution to an air lock?

Blow it back with mains pressure water. I have this issue with my hot/cold line. If I drain the hot/cold pipework (not mains cold) then after refilling the flow is rubbish. I have a bit of hose that I link hot and cold (mains) basin taps with. Turn on hot full then cold full to blow the air back. I can tell when it works as then the hot runs full bore again. Of course the fun part is keeping the hose on the taps since if it comes off it is water everywhere :eek:

southcoastrgi

If you have rusty bits then I would say you have iron pipework somewhere & this is rust that is coming off the inside of the pipe, made worse by the acidic DS3 you have used, I'm guessing you have now filled up your taps & pipes with rust which is why it's worse, I have never in 32 yrs in the trade had to do what you have done & I would have been looking elsewhere to find out what your pressure prob was ie high pressure taps on a low pressure system or a twisted flexi or faulty check valve to your taps

Did you read the instructions ?

Descaling an entire hot water system
Instructions for use:

4) Fernox DS-3 should first be dissolved in warm water, at the maximum concentration of 1 kg per 10 litres of water, (minimum concentration is 250 g per 10 litres of water).

7) Turn on the boiler and/or immersion heater and heat the acid solution in the hot water cylinder to a moderate temperature (50-60oC / 120-140oF) and keep at this temperature for a minimum of 4 hours (max 12 hours).

8) Open all hot water taps briefly every 10-15 minutes, allowing ½ - 1 pint of acid solution to run into a plastic container.

9) Finally, turn off the boiler and immersion heater, and drain the hot water system completely. BALE OUT any residual water from the cold water storage tank as this may contain some DS-3 below the feedpipe connection.

10) When disposing of spent DS-3 solution it is best neutralised with Fernox Superconcentrate System Neutraliser.

ed110220

southcoastrgi wrote: »

If you have rusty bits then I would say you have iron pipework somewhere & this is rust that is coming off the inside of the pipe, made worse by the acidic DS3 you have used, I'm guessing you have now filled up your taps & pipes with rust which is why it's worse, I have never in 32 yrs in the trade had to do what you have done & I would have been looking elsewhere to find out what your pressure prob was ie high pressure taps on a low pressure system or a twisted flexi or faulty check valve to your taps

Did you read the instructions ?

Descaling an entire hot water system
Instructions for use:

4) Fernox DS-3 should first be dissolved in warm water, at the maximum concentration of 1 kg per 10 litres of water, (minimum concentration is 250 g per 10 litres of water).

7) Turn on the boiler and/or immersion heater and heat the acid solution in the hot water cylinder to a moderate temperature (50-60oC / 120-140oF) and keep at this temperature for a minimum of 4 hours (max 12 hours).

8) Open all hot water taps briefly every 10-15 minutes, allowing ½ - 1 pint of acid solution to run into a plastic container.

9) Finally, turn off the boiler and immersion heater, and drain the hot water system completely. BALE OUT any residual water from the cold water storage tank as this may contain some DS-3 below the feedpipe connection.

10) When disposing of spent DS-3 solution it is best neutralised with Fernox Superconcentrate System Neutraliser.

Hi, yes I followed those instructions on the Fernox site. The only thing I did slightly differently was to run the descaler through the system till the coloured water came out of the taps. Ie if you just open the hot taps till the water has run out you still have a hot water cylinder full of fresh water if you follow the Fernox instructions to the letter with this system type.

Since then I covered the kitchen tap (a mixer tap) with my thumb, turned on the hot water and then the cold water (mains pressure) at the same time to force the cold water back up the hot pipe and this has improved it a lot, so I guess there was an air lock or something like that.