HW Tank Conversion: open vented to mains

[tomton]

Hi,

I was planning to install thermostatic shower/bath mixer tap but it needs min. 1bar water pressure to work properly. I bought water pressure gauge to check pressure and cold is 2bar but hot is 0

Question:
Is it possible to feed HW cylinder from mains without F&E tank so i can get HW mains pressure.
I know it needs Pressure Temperature Release Valve to be installed but don't know how the conversion should be done.

CURRENT SYSTEM:
Glowworm Fuel Saver MKII (old but works fine) GroundFloor
HW Tank GroundFloor (22mm feed but I'm not sure about mains)
HW/GCH F&E Attic

Thanks in advance...

 

[kirkgas]

Q can you convert conventional cylinder to mains
A NO

 

[simond]

I went to a quote the other day where a plumber had done this.

I only realised what he had done after I noticed how the pipes were all misaligned on the top of the cylinder.

Basically the bottom invert had popped outwards lifting the whole cylinder about 12" higher.

The lady said there was nothing wrong with her plumber and it was working fine. Never did get the boiler replacement job.

To the OP; buy an unvented cylinder, they are designed for the task, you will find lots of threads here about water flow rate checks, and the need to get a qualified plumber in to fit it all up and register it.

 

[TicklyT]

You could, in much the same way as you could build a thermoneuclear device in your garden shed....

Unvented cylinders are of heavier construction to cope with the loads they are subjected to, and need to be fitted with a number of different safety devices to prevent accidents. They are subject to many regulations regarding installation and maintenance to ensure their safety.

Instead of attempting to pressurise a vented hot water cylinder (which will invite yet another link to that clip of the exploding water heater ) you could consider running a seperate gravity cold feed from your CWST and installing a shower pump, or selecting a thermostatic mixer designed to work with low pressure gravity systems, with water pressures around 0.1 Bar

Your hot water system pressure will be higher than 0, just not high enough to be detected by your gauge.
Measure the vertical height from your shower head position to the bottom of your CWST in Metres, and divide by 10. That will be near enough to your hot water pressure in Bar.

Some manufacturers make showers that use a venturi to boost the hot water pressure using the cold supply pressure.

 

[savilleorange]

Interesting replies.
Yes it is possible to draw mains pressure hot water from your existing HW tank. There is a small box available with a heat exchanger and a pump which turns main cold water into mains hot water. The water inside the cylinder stays inside and remains unvented and unpressurised. When you turn a hot water tap on, a flow sensor inside the box will switch the pump on to circulate hot water from the top of the cylinder into a plate heat exchanger and then back to the bottom of the cylinder.This stops when the hot tap is closed.

A corrosion inhibitor has to added to the entire cylinder to stop the pump from rusting. Your existing cold water tank and vent pipe will stay.

The box hardly measures about 12-14 inches (height and width) and is about 5 inches deep. I fitted one in my daughters house to supply HW in the bathroom in the loft. Still working after 4 years.

 

[simond]

I take it you are talking about the DPS box, we used a large one to heat a church font off an industrial boiler.

 

[BigBurner]

Q can you convert conventional cylinder to mains
A NO

He can if he buys a heat bank coversion kit from DPS.

 

[BigBurner]

Interesting replies.
Yes it is possible to draw mains pressure hot water from your existing HW tank. There is a small box available with a heat exchanger and a pump which turns main cold water into mains hot water. The water inside the cylinder stays inside and remains unvented and unpressurised. When you turn a hot water tap on, a flow sensor inside the box will switch the pump on to circulate hot water from the top of the cylinder into a plate heat exchanger and then back to the bottom of the cylinder.This stops when the hot tap is closed.

A corrosion inhibitor has to added to the entire cylinder to stop the pump from rusting. Your existing cold water tank and vent pipe will stay.

The box hardly measures about 12-14 inches (height and width) and is about 5 inches deep. I fitted one in my daughters house to supply HW in the bathroom in the loft. Still working after 4 years.

Yes, available from DPS and far cheaper than an unvented cylinder and can be DIYed. It is all low pressure except through the plate heat exchanger.

The existing cold water tank becomes a very large F&E tank. This is a very cost effective way to get mains pressure hot and cold water.

You can buy the parts and make one yourself cheaper, however the DPS unit comes pre-made in a box, and simple to fit.

The cylinder should last as no potable water will be running through it and it is at low pressure.

Here it is:
http://www.heatweb.com/products/hiflow/hiflowbzinstall.htm

 

[savilleorange]

Well! Well! Well!
So there are plumbers who know about this system. I thought they were all die hard bolt and braces types. My mistake.

 

[Agile]

A corrosion inhibitor has to added to the entire cylinder to stop the pump from rusting. Your existing cold water tank and vent pipe will stay.

The box hardly measures about 12-14 inches (height and width) and is about 5 inches deep. I fitted one in my daughters house to supply HW in the bathroom in the loft. Still working after 4 years.

If you use a bronze pump then you can still leave the hot water cylinder to supply other HW outlets and dont need to dose the water.

However, the simplest solution is still to use a simple shower pump to increase the pressure to the tap.

I would probably use a single ended pump and a pressure reducing valve on the CW supply as thats cheaper and easier to fit.

Tony

 

[tomton]

Thanks for all your replies.

What about this
http://www.screwfix.com/prods/33590...;jsessionid=IZXAQWOGOPHUSCSTHZOSFFY?ts=61183#

i think it might be good solution for my problem. Unfortunately there is no installation diagram but I assume that it goes on HW tank feed and got some flow detector that will switch on when tap open (I might be wrong).

Do you think that thermostatic tap is not going to work at all if pressure to low or it's efficiency will be low.
I assume that pressure is needed to open valve but I couldn't find anything to confirm that.

Tom

 

[BigBurner]

A corrosion inhibitor has to added to the entire cylinder to stop the pump from rusting. Your existing cold water tank and vent pipe will stay.

The box hardly measures about 12-14 inches (height and width) and is about 5 inches deep. I fitted one in my daughters house to supply HW in the bathroom in the loft. Still working after 4 years.

If you use a bronze pump then you can still leave the hot water cylinder to supply other HW outlets and dont need to dose the water.

The only ferrous in the cylinder water is the pump. A bronze pump would be beneficial, however a can of X-100 every 4 years is good enough. Gledhill say you don't need inhibitor but no harm in a can of it.

However, the simplest solution is still to use a simple shower pump to increase the pressure to the tap.

A good shower pump gives 1 bar and a Stuart Turner cost a around £250 min, plus the other bits. They are noisy and don't last long and only do one shower. If you want one that does two showers and more pressure then talk of £450-500.

The DPS box does all the house, not just showers and is easy to fit and quiet.

 

[BigBurner]

Thanks for all your replies.

What about this
http://www.screwfix.com/prods/33590...;jsessionid=IZXAQWOGOPHUSCSTHZOSFFY?ts=61183#

i think it might be good solution for my problem. Unfortunately there is no installation diagram but I assume that it goes on HW tank feed and got some flow detector that will switch on when tap open (I might be wrong).

Do you think that thermostatic tap is not going to work at all if pressure to low or it's efficiency will be low.
I assume that pressure is needed to open valve but I couldn't find anything to confirm that.

Tom

That is a Wilo Smart CH pump.

 

[savilleorange]

Thanks for all your replies.

What about this
http://www.screwfix.com/prods/33590...;jsessionid=IZXAQWOGOPHUSCSTHZOSFFY?ts=61183#

As said, this is a central heating circulator. A shower pump costs in hundreds not in tens.