Sand on the bum in the bath!

[preeves]

I'm not a plumber but managed my own self build last year and now looking for help with a plumbing issue please. We have become aware of a sand like residue in the bathwater which is very irritating. Our hot water system is as follows: A 280 litre Telford unvented thermal store, underfloor heating up and downstairs, and solar hot water backed up by Vaillant condensing boiler. Whole system designed by Rayotec. Seems very efficient - plenty of hot water and a nice warm house but fairly soon after commissioning the system the 'sand' issue developed. When the bath water has drained away about half a teaspoonful of the stuff can be collected. It looks just like sand but I'm assured that it is lime scale. We live in an area where the water is classified as 'moderately hard' (180ppm). Lime scale doesn't appear to be a serious problem generally - very little build up in the kettle or on shower heads for example. The mains water is crystal clear - the sand clearly develops in the DHW coil in the store as the cold water passes through it. To begin with we had no scale inhibitor installed on our system but Telford told us this was a mistake and a thermal store requires one. We therefore had a Salamander in line electrolytic inhibitor fitted a few months ago which appears to have had no effect at all! Telford are puzzled but sent out one of their plumbers who flushed out the DHW coil a few weeks back. (He also changed the blending valve which he said was a type they no longer use - it was as clean as a whistle inside). A lot of 'sand' was flushed out of the coil but, whilst there is now less scale, it has definitely not eliminated it. Two questions: 1) Are we the only house on the planet to have experienced this phenomenon? - it certainly feels like it as everyone we have consulted seems mystified! 2) Is a proper water softener the only solution likely to succeed in getting rid of the scale once and for all? Advice very gratefully received.

 

[stevetheplumber]

i cant belive that scale could be produced in the short period a bath is run within the coil. Ive got a similar set up at home and only a cheapey scale reducer in a hard water area and dont get this problem i would have suggested sand had got into the pipework during installation but i would think it would have washed through by now, have you tried disolving the sand you collect in vinegar just to prove it is lime scale ?

 

[snowhead]

Take a glass of cold mains water at the nearest tap to the stop tap and also a glass of hot water thro the bath tap and compare the 2.

Is the bath plastic or steel / cast?

 

[preeves]

Snowman - Thanks very much for trying to help. I did what you suggested and also ran a couple of baths. A glass of cold mains water is crystal clear as you might expect. A glass of hot water comes out looking exactly like a glass of milk but clears in about 30 seconds. No residue is detectable in this quantity. I also ran a cold bath which was equally clear and clean. The hot bath felt gritty but, as I mentioned in my reply to stevetheplumber above it emptied to leave a very small amount of 'sand' this time. I started this thread up in frustration after my wife reckoned that Sunday's bath felt as bad as ever but I'm not so sure after today. It really is greatly reduced. The bath is plastic by the way.

 

[preeves]

Steve - Thanks very much for replying so promptly. It's interesting (and even more frustrating) that you have almost the same system with no problems. I did what you asked. I put about half a teaspoonful of my 'collection' in some vinegar and - yes - it did dissolve although it took several hours. I though it wasn't going to at first because nothing appeared to happen but, slowly but surely, the crystals got finer and finer until they were gone. I share your view about how such robust crystals can be formed in the few seconds that it takes for the cold water to flow up through the coil in the tank but what else could it be? In the summer the water in the store got very hot (about 80C) due to the input from the solar panels. Do the crystals form more readily at higher temperatures? As you can see in my reply to snowman below the residue in the test hot bath this morning was greatly diminished and I wonder if the flush by Telford's plumber has got rid of a build up and it may slowly clear up. He didn't do an aggressive flush - just a washout into the bath with a hose - so there may be a bit still to go.

 

[stevetheplumber]

it could be the high temps due to the solar making the limescale form as thats the difference in our systems im not up with solar maybe some one else can say if there should be a temperature limit on this system you could have a descale done on the coil if you was local to me id charge a couple of hundred quid for it at least then youd know if it was clear for a while after