10 min wait until hot water flows from tap

sharkie

Hi All,

this should be simple, but I am not sure why it has gone wrong?

When the kitchen tap is turned it, it dribbles (stream of drops), then after 10-15 mins flows normally. Once the hot water runs, the tap can be turned off and straight after on again and the water runs normally, leave the taps closed for 2 mins, and you have to wait approx 15 seconds. Turning on the cold tap seems to make no difference.

My water tank is in the upstairs airing cupboard and the hot water is gravity fed the cold water is straight from the mains.

The sink is designed to have a monoblock mixer tap. On the old monoblock tap, if the cold was opened too far it would start to push the hot water back up into the tank and so could fill the hot tank.

So my old monoblock broke, so now fitted a new monoblock but added a Water Pressure Equalizing Valve and it worked great for a week or so.


I was going to add a Backflow Prevention valve instead, but thought that it would cut down the already limited hot water pressure, and that the above (a) would be a better choice and (b) balance the hot water temp too.

What has gone wrong and what method should I have used to fix the above initial problem?

thanks

ormus

i would try a non return valve in the hot line. near the tap.

make sure you fit it the right way round!

sharkie

ormus wrote: »

i would try a non return valve in the hot line. near the tap.

make sure you fit it the right way round!

thanks and yes, never used one and the water pressure to the tap due to the lack of height was never great, and I was uncertain how much resistance it would offer causing even less presure?

iveco_man

dont fit non return valve on hot if there is no presure now you wont get any water at all from your taps

Canucklehead

Hi,


Kitchen sink mixer/monoblock taps are (or should be ) designed to have a separate flow of hot and cold to the end of the spout.

This overcomes the problem of cross flow due to unequal supply pressures. This applies mainly to sink mixers as mixers for bathrooms are usually from a balanced supply of hot and cold , therefore crossflow is not a problem.

If you have bought a good quality tap this will have that separation.
Check with the manufacturer.
Also check it is designed for low pressure gravity hot.

Take out all the restrictive fittings you have inflicted on the hot supply.

Fit a large bore isolating ball type valve to the hot supply.

Make sure any flexi hoses are not kinked or twisted.

This is probably as good as you will get for a monoblock sink mixer fitted to a gravity supply. You can live with it or convert to mains pressure hot water via a combi or unvented cylinder.


GSR.

sharkie

I am planning to redo it all.

On replacing the first monoblock, my first attempt had a ceramic disk and that made the water have little pressure -slow. I was advised to go for a cheap normal one.

The second one was a b&q el-cheapo and the water mixes in the base where the monoblock meets the spout, rather than separate pipes going up the spout towards the end, so no separate flow. This was the least restrictive one b&q had.

this is the non return valve below, and I am using full bore pegler stop valves on the hot pipe.

ListysDad

Sorry to contradict some of the advice you've already been given (sorry Ormus), but the pressure reducing valve you have already has two non return valves fitted.

CHEAD was spot on in terms of you removing all the resrictions in the HW line too. Personally I'd never use flexi tails in that situation as the bore on them is much reduced. Rigid copper is best in this case. As he says, use decent full bore isolating valves and that's it!

The problems you're suffering are classic symptoms of having too great a differential between hot and cold. When this happens the non retun valve in the HW line gets rammed home by the high pressure of the cold water. The engineers out there will immediately say that can't happen! It can and does because there is a tiny hole designed into the diaphram. This allows the mains pressure to seep into the hot side doing as I described earlier.

NO pressure equalising valve will work properly with a ratio of more than 1:20. So a typical british domestic hot water pressure of say .015 bar means your mains must never get higher than 3 bar. The reality of these devices is that it's nearly always best to fit a pressure reducing valve into the cold side to bring the cold pressure down to say 2 bar. I can guarantee it will then work flawlessly.

Lastly DO NOT remove the check valves as you WILL get other problems if you do.

All this is born of 2 days lost on a customers shower using one and spending hours and hours getting to talk to the actual designers rather than plumbers merchants who couldn't comprehend the question never mind answer it! Once money's been lost the lessons never are...

Hope that solves your issue.

David

botanical

sharkie wrote: »

Hi All,

this should be simple, but I am not sure why it has gone wrong?

When the kitchen tap is turned it, it dribbles (stream of drops), then after 10-15 mins flows normally. Once the hot water runs, the tap can be turned off and straight after on again and the water runs normally, leave the taps closed for 2 mins, and you have to wait approx 15 seconds. Turning on the cold tap seems to make no difference.

My water tank is in the upstairs airing cupboard and the hot water is gravity fed the cold water is straight from the mains.

The sink is designed to have a monoblock mixer tap. On the old monoblock tap, if the cold was opened too far it would start to push the hot water back up into the tank and so could fill the hot tank.

So my old monoblock broke, so now fitted a new monoblock but added a Water Pressure Equalizing Valve and it worked great for a week or so.


I was going to add a Backflow Prevention valve instead, but thought that it would cut down the already limited hot water pressure, and that the above (a) would be a better choice and (b) balance the hot water temp too.

What has gone wrong and what method should I have used to fix the above initial problem?

thanks

'ot water? 'ot water? Ten minutes? Ten minutes? You're lucky to 'ave 'ot water by boy. In my day we 'ad a bucket filled wi' rainwater t' wash in and lucky t'ave it! Young pup! Young generation t'day. I don't know...

ListysDad

:T :T laugh, I almost contemplated buying a round!

botanical

ListysDad wrote: »

:T :T laugh, I almost contemplated buying a round!

mine's a pint and be quick about it lad!

ListysDad

This is Yorkshire! Trousers by Burtons, pockets by Chubb and the loosest shoelaces on the planet... Hey we make Jocks look generous! :beer: