Loft Tanks

[CluelessPaul]

I've recent moved into a home which is served by a conventional gas boiler that feeds the radiators and a cylinder in an upstairs cupboard. I don't understand the plumbing layout and so I'm hoping someone can help me based on what I can post here! Thanks.

There are two water tanks in the loft (neither is jacketed; they both have bits of polystyrene loosely wrapped around them. The smaller one is only about 30x45cm and contains very nasty looking 'water'. It doesn't appear to feed any taps (thank goodness) and may be completely redundant judgeing by the stagnant state but I'd like to understand what it might be... The bigger one is much bigger (a few feet, almost square) and full of clean cold water. The odd thing is that when I run my cold taps the water doesn't appear to come from this tank but straight from the rising main instead. When I run my hot taps however this tank starts to drain which I guess can only mean that the boiler is drawing it, and heating it to pipe to the emptying hot water cylinder.

This seems like a strange arrangement and I'm wondering why a cold tank in the loft wouldnt feed the cold water taps and why it would feed the boiler instead (which is actually in my garage!).

I can try and answer questions if I haven't supplied enough detail but they will have to be words of one syllable. Grateful for any info.

 

[Ric2013]

What it sounds like is the large tank ("cistern") feeds your vented cylinder which is heated by the boiler. Essentially that cistern is what gives your hot water enough pressure to come out of the taps while allowing the water to expand when heated. Some houses do use a cistern for cold taps too, but generally the drinking water (kitchen) is straight from mains because tanks in lofts are a potential breeding ground for bacteria. Basically, mains water is cleaner!

The smaller cistern is likely to be a feed and expansion cistern for the boiler and radiators. The water in the boiler does not come out of your taps: there is a coil in the cylinder that allows a heat transfer, with the radiator and boiler water not being changed, but always the same water, same as a car's cooling system which only needs topping up very occasionally to allow for any slight leakage. When you heat water it expands, and it contracts as it cools. This cistern allows the water to do this without anything exploding.

If the boiler water cistern "feed and expansion" is full of crud, particularly if the crud is brownish rather than blackish, it may be worth getting a local plumber/heating installer to comment on whether you have enough corrosion inhibitor in the system and to give you a price on upgrading the cisterns - particularly the one feeding your cylinder - to so-called byelaw 30 (fit proper lids, and anti-insect devices).

 

[CluelessPaul]

Thanks very much for the reply and clear info.

Just to confirm that I understand it right then; as I draw hot water from the taps the cylinder is replenished with cold water from the cistern and this is then heated indirectly by water from the boiler?

Someone I spoke to mentioned that I might be able to jacket the tanks/cisterns but I'm not convinced they know a lot more than me.. Apart from the happy feeling of having new ones is there any reason why I would replace them rather then jacket them?

 

[Ric2013]

Thanks very much for the reply and clear info.

Just to confirm that I understand it right then; as I draw hot water from the taps the cylinder is replenished with cold water from the cistern and this is then heated indirectly by water from the boiler?

Someone I spoke to mentioned that I might be able to jacket the tanks/cisterns but I'm not convinced they know a lot more than me.. Apart from the happy feeling of having new ones is there any reason why I would replace them rather then jacket them?

Your understanding is correct.

It is rare for there to be a reason to replace cisterns. They are normally plastic and do not usually tend to wear out. Lids can often be sourced to fit existing cisterns as cistern design is not something that changes very often. Even if you bought new ones they would only come with cheap plastic-bagged fibreglass jackets and you can buy these separately/make better insulation boxes from polystyrene etc.

 

[Thank you!]

Your understanding is correct.

It is rare for there to be a reason to replace cisterns. They are normally plastic and do not usually tend to wear out. Lids can often be sourced to fit existing cisterns as cistern design is not something that changes very often. Even if you bought new ones they would only come with cheap plastic-bagged fibreglass jackets and you can buy these separately/make better insulation boxes from polystyrene etc.