Back to a vented DHW tank?

[Deejay_2]

We intend refurbishing our bungalow sometime in the future.

In the meantime we have a 12 year old Worcester Bosch combi boiler which is serviced annually and seems to be working well.  We have a recurring problem with our 3 year old Mira Mini Duo shower which started to "scream" when the water became hot and over time the flow reduced.  Plumber said we needed a new thermostat (£300+).  I sourced, he fitted.   Problem remained.  He removed the whole thermastatic valve from the pipe inlets in the shower and it turned out to be sand in the hot water inlet.  So new valve redundant.  This same problem now happens regularly after around 3 months and because I witnessed the sand clearance by the plumber, we can now do this ourselves.  This has been going on for around 2 years.

Others on the internet with same problem put this down to a boiler problem but our very experienced plumber never mentioned this and has since serviced the boiler twice. 

We have no back-up hot water if the boiler breaks down.  So:

1     Would like to reinstate cold water tank in loft on existing plynth.  I presume most of pipework is still in place.  There are only 2 of us and we have one shower room, no bath, and one kitchen.

2     Would like a vented tank with immersion heater(s), we have cupboard space in the kitchen (where the original boiler was I think).  This would mainly be used as back up should the boiler break or the gas is cut off or rationed (which could happen).

3     We don't want to change the boiler at this point as it is not over-used and I think has quite a few more years to go.  Could we install an INdirect cylinder not connected to our combi boiler and just use the immersion facility so the cylinder is ready to be connected to a new non combi boiler in the future.  If not we would have to presumably change the cylinder from direct to indirect in the future.

4    We have a thermostatic Mira Mini Duo shower - will this still work from an unvented cylinder.   

We just want simple and straightforward, and the least expensive but not the least efficient.  

Any advice would be appreciated.

[JohnMo]

First a boiler cannot produce sand, it can produce other deposits, lime scale and calcium etc.

 

If it is really sand it is likely it's coming in with the mains water, so something as simple as a filter in the line will address that.  What does your kettle look like inside as that goes through same process as a boiler, are there any deposits?

 

One way to test, draw of cold water in a clear jug, leave for an hour or so, are there any deposits?  Draw of hot water do the same compare results.

 

If you are producing deposits in the hot water that are not there in cold water, you need to treat the water prior to heating, something like a combimate, adds a food safe chemical to the water to stop deposits forming, or a water softener if in a hard water area.

 

Installing a cylinder which is not used often if at all, could be unhealthy as you are really having a place where water can be stagnant - not good for your health.

 

If you are going a cylinder route you really have two choices, convert your combi to a system boiler.  Basically cap off the cold and DHW feeds.  But install an unvented cylinder so you get decent DHW flow.  Then have your immersion ready to use should the need arise.  Or install a small cylinder upstream of the combi, so all cold water passes through it.  A solar diverter valve could be placed between the cylinder and the combi.  Such as this

 

https://www.bes.co.uk/thermostatic-solar-valve-kit-with-bypass-21082/

 

Then if the immersion is on and the cylinder is above 43degs all water bypasses the combi.

 

 

 

[Deejay_2]

OK.  We appear to be in a hard water area according to the Yorkshire Water postcode search.  I've taken samples of both hot and cold water and no sediment whatsoever after an hour. 

 

I would say it's definitely sand in the incoming hot water pipe in the shower as it is red in colour and looks and feels like sand plus the plumber said it is sand but offered no explanation.   We have a Brita filter kettle so can't see the bottom, but I seem to remember with other kettles having build up of calcium type stuff in the bottom.  Is it possible to continue using the combi boiler and have the vented cylnder as a completely separate entity but use it a few times a week to keep the water moving.  Or as you seem to be saying, could we convert the boiler to a heat only boiler (central heating) and use the cylinder for all our hot water as gas is no longer cheaper than electricity.  I'm not sure what the difference is now as we are still on a fixed rate until next year - stroke of luck really.  

I would prefer the simplest way possible and am not sure about the complexity of an unvented cylinder.  

We shall be reviewing our heating and water requirements in the future when we refurbish the bungalow so this is an intermediate measure as I am not comfortable being totally reliant on gas for our dhw.

Thank you for your advice which was very helpful.  Any further thoughts would be appreciated.

[JohnMo]

When you convert the boiler it would still heat the cylinder as a system boiler does using a y plan or similar.  There is a big difference in gas and electricity prices, I pay 7.33p for gas and 30p for electricity.

 

Your easiest is the second option

 

If you want vented install something like this https://www.toolstation.com/indirect-hot-water-cylinder/p62376 in the the cold water supply to the combi.  Install 3kW immersion and use the diverter valve mentioned previously.  Job done.  Normal cold water passes through cylinder and diverter valve to combi.  Combi fails switch on immersion, once up to temp water diverts past combi and hot water to taps.

[Deejay_2]

Your last paragraph is the exact solution I was looking for - thank you so much.  So we can use our combi boiler with an indirect cylinder.  The cylinder water will be heated by the boiler but should we end up with no gas for any reason we shall have an immersion heater to fall back on.  This will still require a header tank and may also require a pump for the shower.  I now know what to discuss with the plumber.  

I have spent quite sometime researching the options but your post has fitted the jumble into something I can understand.  Can you let me know if I have misunderstood anything.  

I'm so grateful.  

 

[JohnMo]

No I don't think you have read what was written correctly.

 

This cylinder will only ever be heated by the immersion.