Descaling Unvented Cylinder

[MJNewton]

We live in a 2007-built housing estate and over the past few years I've seen a number of unvented cylinders being replaced and, having grabbed one of the plumbers doing a job recently discovered that in that particular case (and perhaps therefore others too) the issue has been down to the cylinder scaling up and blocking the inlet at the bottom. These particular cylinders - Range Tribunes - appear to have an inlet whose design is meant to help minimise destratification but is seemingly vulnerable to to the consequences of limescale.

 

I was wondering: is it practical to descale such a cylinder and, if so, how? I do wonder if it might actually risk causing more harm than good e.g. dislodging some scale that then blocks something, or causing a leak around the immersion if the chosen might involve its removal to hoover out scale etc. Recognising the G3 restrictions about working on these things consider it a hypothetical exam question scenario.

 

Also, I am considering fitting a whole-house water softener (with bypass for the kitchen tap) and so presumably this would prevent further scaling occurring. Water softener manufacturers claim that it will gradually remove existing scale too - is this true? Might that be a safer approach (more gradual, no physical disruption to the cylinder and its fittings etc), and perhaps could be considered to represent value for money given that it'll hopefully negate the need for eventual cylinder replacement (at least for scaling-related issues)?

[JohnMo]

2 minutes ago, MJNewton said:

Also, I am considering fitting a whole-house water softener (with bypass for the kitchen tap)

I just use https://www.bwt.com/en-gb/products/protection-for-heating-systems/combi-care/22-mm-combi/

 

Have it in the inlet pipe to the UVC. Change the cartridge once a year.

 

To descale fully, you really need to do same as you would your kettle and dissolve the stuff, flush away. Not sure it's something I would contemplate on a big cylinder.

[MJNewton]

52 minutes ago, JohnMo said:

I just use https://www.bwt.com/en-gb/products/protection-for-heating-systems/combi-care/22-mm-combi/

 

Have it in the inlet pipe to the UVC. Change the cartridge once a year.

 

I'd seen them but glossed over them assuming they weren't intended for me - perhaps thrown by the common use of the word 'combi' in the names of these products.

 

So, would I be looking to supply the whole house through one of these (including taps for drinking from) it just the hot water side of things? I must say, even though we've got very hard water we don't find the cleaning of taps and other wet surfaces a particular problem - the main concern is scaling of the cylinder given how expensive it (and its (re)installation) is.

[Gone West]

2 hours ago, MJNewton said:

I was wondering: is it practical to descale such a cylinder and, if so, how?

When living in the temporary bungalow while building the house our vented DHW cylinder sprung a leak. I took it out, removed the immersion and tipped out a lot of loose scale that was just lying in the bottom of the cylinder. It was a very hard water area.

[MJNewton]

4 minutes ago, Gone West said:

When living in the temporary bungalow while building the house our vented DHW cylinder sprung a leak. I took it out, removed the immersion and tipped out a lot of loose scale that was just lying in the bottom of the cylinder. It was a very hard water area.

 

I did think removing the immersion might be a good starting point, if only to give my visible access to gauge what state we're in. If I could get a vacuum hose in (no chance of removing the cylinder - it is too piped in) that might help too. Would need to be confident I could re-seal the immersion though so need to work out what type of seal it actually uses. Knowing my luck though the current immersion will be seized in place and I'll end up deforming the cylinder trying to unscrew it!

Edited July 17 by MJNewton

[marshian]

Several years ago I had to replace an immersion on a 118 litre vented copper cyl - the mount for the immersion had clearly been annealed over the life of the cyl and it started to twist and the copper was rucking up - continuing to try to remove the dead immersion heater would have resulted in fracture.

 

It was easier to replace the whole tank so I did for one with an integral foam jacket (old one used to wear two puffer jackets)

 

None of the metal reclamation yards near me would take the tank unless it was opened so I cut it open

 

The level of scale in the tank as a result of moving it around was up to the top of the HW heating coil - the heating coil had maybe 10mm of scale around it. (We are in a hard water area)

 

Explained why we frequently ran out of HW after a bath was run and why heating water used to have to be done at the same time as CH or would have to be done twice a day in the summer for an hour each time

 

Fitting a new tank the water heated in 30 mins and could be done once a day and we haven't ever run out of HW on any day

[MJNewton]

That's interesting @marshian, and the kind of thing I was concerned. That said, the tank is stainless steel and the immersion appears to be sealed with an o-ring so finger's crossed that might mean it won't be seized in place. After 18 years though anything could've happened!

 

The dilemma is do I wait until there's an issue (and risk not easily being able to run solution through all the component parts which might be helpful) or perform preventative maintenance (and risk causing a different problem in the process!).

[marshian]

14 minutes ago, MJNewton said:

That's interesting @marshian, and the kind of thing I was concerned. That said, the tank is stainless steel and the immersion appears to be sealed with an o-ring so finger's crossed that might mean it won't be seized in place. After 18 years though anything could've happened!

 

The dilemma is do I wait until there's an issue (and risk not easily being able to run solution through all the component parts which might be helpful) or perform preventative maintenance (and risk causing a different problem in the process!).

 

There is a dilemma there for sure

 

For me prevention is always better than cure - so I'd investigate the internals however I could - Drain down and remove outlet or inlet pipes and use one of those cheap plug in camera probes that work with a phone?

[marshian]

5 hours ago, MJNewton said:

Also, I am considering fitting a whole-house water softener (with bypass for the kitchen tap) and so presumably this would prevent further scaling occurring. Water softener manufacturers claim that it will gradually remove existing scale too - is this true? Might that be a safer approach (more gradual, no physical disruption to the cylinder and its fittings etc), and perhaps could be considered to represent value for money given that it'll hopefully negate the need for eventual cylinder replacement (at least for scaling-related issues)?

 

Oh I missed this bit in your original post - we did exactly that (fitted a water softener) after seeing the scale in the tank

 

It did exactly that - dissolved and removed scale in other parts of the system (in our case the cold water header tank in the loft (outlet fitting) and we had an unexpected surprise a year later)

[MJNewton]

Just now, marshian said:

 

Oh I missed this bit in your original post - we did exactly that (fitted a water softener) after seeing the scale in the tank

 

It did exactly that - dissolved and removed scale in other parts of the system (in our case the cold water header tank in the loft (outlet fitting) and we had an unexpected surprise a year later)

 

Thanks for that! I did wonder if it was just overblown marketing blurb, or perhaps something that is technically correct but in practice might take decades or something.

[marshian]

Just now, MJNewton said:

 

Thanks for that! I did wonder if it was just overblown marketing blurb, or perhaps something that is technically correct but in practice might take decades or something.

 

We'd lived here 20 years and never had so much of a drop of water on the coldwater tank stand.

 

The boards were soaked, as was the plasterboard beneath it and the loft insulation around it. I think we got lucky as we saw no tell tale marks on the ceiling - I just happened to be going up in the loft for the Xmas Decs.

[MJNewton]

Oh I see - the removal of the scale caused a leak?

[marshian]

13 minutes ago, MJNewton said:

Oh I see - the removal of the scale caused a leak?

 

Yep 100% - I think when the fitting was installed the scale built up around it and the rubber seal gradually degraded - leaving just the scale protecting stopping any potential water from getting thro - the combination of a degraded rubber seal on the back of the fitting sealing it to the tank wall and the gradual removal of the scale prompted the water leak.