Converting to Direct Mains System

Postby Unclesatan » Tue Jun 24, 2008 9:15 pm

Hello, this will be my first post so hello everyone.

I've done a search on this but come up empty handed so please forgiveme if I've missed a previous topic.

My house has an Unvented Hot water Cylinder and a lot of the cold taps seem to be mains fed, however I still have a header tank in the loft which I pressume is feeding the toilets and maybe the upstairs taps.

Not only does this make it almost impossible to fill the bath in a reasonable amount of time, it also means I've got a huge tank in the loft not really doing much.

What would be involved in making the rest of the cold water system 'direct' so I could remove the tank all together.

With my limited knowledge of plumbing it seems the simplest way would be to connect the rising main to the remaining low pressure pipes through a non-return valve. Although this seems too simple and I'm sure somebody will be able to tell me why this couldn't or shouldn't be done.
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Simply Build It

Postby plumbbob » Wed Jun 25, 2008 10:35 pm

Maybe the only reason the tanks were left in the loft is if they are feeding toilets, the ball valves would be set for low pressure. You may have to replace them if the conversion parts are not to hand.

It does seem a little odd that half the system has been left at low pressure.

On the face of it apart from the problem with the toilet, you could just remove the tank and connect the riser feed directly to tank outlet.
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Postby Unclesatan » Thu Jun 26, 2008 9:08 am

[quote="plumbbob"]the ball valves would be set for low pressure. You may have to replace them if the conversion parts are not to hand.

Thanks for your reply.

The toilets have been replaced within the last couple of years so parts for them shouldn't be an issue.

Is there anyway I can check to see if the valves are for low or high pressure before I connect them.

I also had another look in the loft and noticed the there was a feed for the shower, which has it's own pump does that need low pressure or can they generally work off mains as well. Actually I might not even nrrd the pump if both hot and cold become mains pressured.
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Postby plumbbob » Thu Jun 26, 2008 4:34 pm

If the ball valves have been working on a low pressure system, they would have had the high pressure nozzles exchanged for the low pressure ones. I am not sure you can buy the nozzles separately so unless you have the parts to hand, the valves will need replacing again.

Now you mention a pump in the shower line makes me wonder exactly what type of system you have. I had assumed the hot water was pressurised and only the cold feed to the bath and toilet was at low pressure.

If you have a traditional hot water cylinder (see the link below), they are only designed to work at low pressure therefore you can only connect the cold bath and basin taps and toilet to the rising main. You would need to keep the header tank to supply hot water to taps and hot and cold to the shower pump. ... 071&m=1228
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Postby Perry525 » Thu Jun 26, 2008 7:48 pm

I would advise against taking that cold water tank away, in fact I propose that you use it!

The first thing to consider is your mains water pressure.

The unfortunate thing about your system is, that you can only get out whatever water is in the main at the time.

Is its pressure high enough to run three taps at the same time, with a decent amount of water coming from each?
Or, does it just dribble out of two and nothing from the third?
Can you run a bath in two or three minutes?

Is the water pressure high in the monring when everyone is using the water?
Can you wash the car, use the washing machine and run a hand basin of water, take a shower, all at the same time?

The reason people had large tanks in their lofts, was to have a supply of water in an emergency. And an additional back up supply to feed more taps at the same time, than can be done from a mains feed such as yours. It could be supplying masses of low pressure water.

You are on the main, and an old main bursts up the road - you have no water to flush the loo,to wash the children, to make a cup of tea!(the hot cylinder will be full but, you cannot use it)
If you have no water, you may find yourself touring the country looking for an open supermarket at two in the morning to find bottled water to wash your baby.

Flushing the loo with expensive bottled water is no pleasure.

First, take a look at your family, do you know where each of them is at every moment, if you are running the dishwasher and the washing machine can someone shower, without loosing the water, being left covered in soap with just a dribble of cold water? Or do they have to wait?

If that tank was used properly and connected with the correctly sized pipes for your home and family..............

Look at the size of the pipes attached to the cold water tank. There could be a 28mm pipe to a open vent hot water cylinder and another 28mm pipe serving the bath and toilet. A 15mm pipe direct from tank to the shower.

The kitchen sink, washing machine, dishwasher, hand basins will all be supplied direct from the main. But, if you had a drinking fountain by the handbasin that too could be low pressure.

That cold water tank in the loft, could change your life.
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Postby htg engineer » Fri Jun 27, 2008 8:35 am

The stored cold water should not be used for drinking. That is why every kitchen is mains fed. You will not a find a kitchen sink that is tank fed.

Every water company states that they can only guarantee water is safe for drinking if it's straight from the mains tap.

Also you cannot pump mains cold water. Check the shower can be used with mains pressure.

If you have stored hot water feeding the shower, you cannot have mains cold water feeding the shower it has to be tank fed. This is for safety reasons, if you have red hot water supplying a shower and for some reason your cold mains is turned off or the fire brigade come into the street and open up the mains for water - you or a child could be scalded.

You'll need to think about this one. If the tank isn't in the way, isn't leaking, shower works, heating and hot water works - leave it alone until you decide to upgrade the whole system, then you can choose the right shower, boiler etc etc

htg engineer
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Postby Unclesatan » Fri Jun 27, 2008 11:11 am

PLumbob, thanks for the info. I was under the impression I had an unvented cylinder, but It appears that I dont as my cylinder looks like the one in your link. Should a low pressure cylinder have an expansion tank? As mine has one fitted?

Perry525, there are only 2 of us in the house so our water needs aren't that great. On balance I'd like to free up the loft more than I'd worry about the occassional inconvenience of loosing mains water, but I will keep some bottled water on hand just in case. I will also need to look at the water though as it takes about half an hour to fill a bath with the current set-up.

htg engineer, after plumbob's post it appears that we don't have a direct hot water system so I'll be following your advice on holding off on conversion untill things need replacing. In the mean time I'll probably clean the tank, check the pipes and look into moving the tank to a better possition in the loft.
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Postby Perry525 » Fri Jun 27, 2008 7:58 pm

Fair enough.
Take a look inside the tank and check that there are no dead birds blocking the outlet pipes.
Check that the pipes are big enough, you need a minimum of 22 mm to the bath.
Check there are no partly tuned off stop cocks between the bath and the cold and hot water tanks.
Check under the bath that there are no stainless steel flexible connectors to the taps as these constrict the flow - if there are replace them.
Check the size of the bath taps are they full bore 22mm?

Finally, consider, you will not live there for ever!
Consider the set up from the point, will this help me to sell?
Best of Luck
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Postby plumbbob » Fri Jun 27, 2008 9:05 pm

My guess is you only have a pressurised heating system and the DHW side is at low pressure fed from the header tank. This is acceptable with this type of cylinder as only the heating coils are pressurised.

It would still make sense to change the feed to the cold bath and basin tap to mains as that would probably help with the speed of filling. Having said that, it is unusual to see why it should take that long to fill the bath. Have you checked the isolator gate valves? One may only be partially open or seized. Check the one feeding the hot supply and ensure it opens and closes fully, and doesn't just keep turning.
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