Controlling Hot Water Cylinder Temperature

dubmark74

I have a question about how to control the temperature in my hot water cylinder. I can heat my cylinder using the electric heating element or the gas central heating. The problem i have is that when using the central heating i cannot control the temperature, it heats up very hot and the hot taps are too hot to use. I've traced the pipes and there is no motorised valve on the central heating supply to the cylinder. There is however a hand valve which is part closed. If i close this a bit more will it reduce the temperaure? Any help appreciated.

jimjimt

No it will not reduce the water temperature. it is used to balance the flow of water between the radiators and cylinder. If you turn it down low it will slow down the water heating up but not the final temperature.

You could turn down the thermostat on the gas boiler. Also check that it is working and not over heating. This will also turn down the heat to the radiators.

Some options for controlling your hot water are,

Motorized valve and cylinder thermostat.

Mechanical thermostatic cylinder valve.

Thermostatic mixing valve for controlling the hot water coming out of the cylinder.

dubmark74

Great, thanks for this Jim, looks like i have the cheapo option. Some questions on your options if you have time:

Motorized valve and cylinder thermostat: would this have to be tied into the boiler. what would happen if the radiators were off (these have motorised valves) and the cylinder inlet valve closed. Would you need to shut down the boiler. Also, my cylinder is one of the ones that comes insulated. How do i put a stat in this.

Mechanical thermostatic cylinder valve: How does this work, stops water once the cylinder is hot?

Thermostatic mixing valve for controlling the hot water coming out of the cylinder: Sounds like the easiest option. leave cylinder as is and control water temperature coming out, i assume by mixing with cold water. I have a pump fed off the cylinder also, would this be a problem?

jimjimt

The motorized valve would have to be wired correctly to the gas boiler. A slot would have to be cut out of the cylinder insulation to allow the cyl stat to strap to the cylinder. When the cylinder heats up the gas boiler shuts down.

The mixing valve is like a shower valve on top of the cylinder. I never actually install one where the pump is coming off the top of the cylinder so I do not know how that would react. Should be ok.But instructions would have to be read before install. Yes you would need a cold supply to the mixing valve also.

The easiest way to do it is using a mechanical thermostatic cylinder valve it works very similar to a thermostatic radiator valve with options from 1-5 and you strap a small probe to the cylinder. But it would not shut down the gas boiler.

The best option is to use the motorized valve if it can be wired correctly to the gas boiler making use of all 5 wires on the motorized valve to wire correctly.

Dardania

The mechanical valve to regulate it is something like this: http://www.heatingcontrolsonline.co.uk/acl-drayton-15mm-2way-tapstat-p-189.html

Just to note, you should keep the cylinder temp above 60 celcius to avoid legionella bacteria growth...it's alright to mix the water down to a usable temp at the tap. Maybe a better solution would be to get mixer taps?

cikearney

For the control of the temperature in a hot water cylinder ther is no need to wire stat and MV to the boiler, presuming there is a bypass on the system.

Take a spur from immersion switch feed the live to the stat and switch to the MV i have done this before and has worked great, especially from a cheapo pov

dubmark74

Really good information, thanks to all.

So i think i'll go with the thermostatic cylinder valve, seems like the easiest option.

I'm surprised you need a stat on the cylinder for this. I would have thought you could just set the temperature on the valve and this controls the water temperature entering the cylinder and therefore the cylinder temperature.

Dardania

dubmark74 wrote: »

Really good information, thanks to all.

So i think i'll go with the thermostatic cylinder valve, seems like the easiest option.

I'm surprised you need a stat on the cylinder for this. I would have thought you could just set the temperature on the valve and this controls the water temperature entering the cylinder and therefore the cylinder temperature.

The cylinder will cool over time, so you need to let more heat into it.

To be absolutely clear, this valve goes on the Low Pressure Hot Water return feed from the cylinder...and not on the Domestic Hot Water supply from the cylinder to the taps. The thermostat is on the cylinder because that is the process you want to be controlled - the LPHW feed is the means by which you control it.

Also, look into mixing taps - might make it easier to deal with. All things going well, you'll be delviering water at ~60C (insteadof ~ 70C to 80C as presently) so it can still be quite hot at the taps.

dubmark74

Dardania wrote: »

To be absolutely clear, this valve goes on the Low Pressure Hot Water return feed from the cylinder...and not on the Domestic Hot Water supply from the cylinder to the taps. The thermostat is on the cylinder because that is the process you want to be controlled - the LPHW feed is the means by which you control it.

Just so im sure, the LPHW return feed is the pipe that the central heating water flows out of the cylinder from. How do i know which one is the return, does it flow in the bottom of the cylinder and out near the top.

Dardania

dubmark74 wrote: »

Just so im sure, the LPHW return feed is the pipe that the central heating water flows out of the cylinder from. How do i know which one is the return, does it flow in the bottom of the cylinder and out near the top.

Generally, yes (heat rises so its logical to flow to the bottom to heat the greatest volume of water in the cylinder). A way to check is to let both the LPHW and contents of the cylinder go cold, then switch on the boiler - the first pipe to heat is coming from the boiler

jimjimt

In your cylinder you have a coil which separates your heating water from your domestic hot water.

The heating water from your gas boiler will enter or should enter on the top pipe of the coil the flow.
As it cools down through the coil it returns back to the gas boiler after transferring its heat to the domestic hot water on the bottom pipe of the coil the return pipe.
(exceptions to the above on some stainless steel pressurized cylinder.)

As you have a gas boiler it is most likely you will have a pressurized heating system and as such it will not be low pressure in the pipe work and coil of the cylinder.

For your own safety you should hire a Plumber/RGII to install your thermostatic cylinder valve and insure your gas boiler can pump and cut out safely when used with the TCV.

dubmark74

Sorry to go on about this but i just wanted to be sure what the option is.

From reading the posts above, i don't need to control the boiler when the valve closes provided i have a bypass. Porblem i cannot see if i have a bypass as the pipes go from the tank under the floorboards. Is there a way of checking this without lifting the floor. What is the likelihood of not having a bypass.

Thanks.

jimjimt

You may to install an automatic bypass valves as well. As such your cylinder was the open circuit and it was your bypass.

This is why if possible to use a mortised valve and cylinder thermostat to control your hot water. When your cylinder heats up it shuts down your gas boiler if wired back to the boiler correctly.

Have a look at the following which you may need to install. It is a automatic bypass valve. Plenty of similar products on the market.


http://www.danfoss.com/Products/Categories/Group/HE/Radiator-Thermostats/Automatic-Bypass-Controls/ac15982c-7908-4f0b-8c23-aeddb11e196b.html

Dardania

jimjimt wrote: »

You may to install an automatic bypass valves as well. As such your cylinder was the open circuit and it was your bypass.

This is why if possible to use a mortised valve and cylinder thermostat to control your hot water. When your cylinder heats up it shuts down your gas boiler if wired back to the boiler correctly.

Have a look at the following which you may need to install. It is a automatic bypass valve. Plenty of similar products on the market.


http://www.danfoss.com/Products/Categories/Group/HE/Radiator-Thermostats/Automatic-Bypass-Controls/ac15982c-7908-4f0b-8c23-aeddb11e196b.html

What model is your boiler? Sme of them have it built in

dubmark74

Dardania wrote: »

What model is your boiler? Sme of them have it built in

Vokera Mynote 16E

Dardania

dubmark74 wrote: »

Vokera Mynote 16E

Per the manual: http://www.vokera.co.uk/wp-content/uploads/2011/09/mynute-12-16-20e-installation-and-servicing-manual-copy.pdf it has an automatic bypass.

dubmark74

Dardania wrote: »

Per the manual: http://www.vokera.co.uk/wp-content/uploads/2011/09/mynute-12-16-20e-installation-and-servicing-manual-copy.pdf it has an automatic bypass.

Always read the manual first. Below seems to indicate that it is preferable to have a bypass but not essential. Anyway, i'm now inclined to go with the suggestion of a motorised valve and tank stat, should be fairly straightforward.

I'd like to thank all for taking the time to help, much appreciated.

The appliance has a built-in automatic by-pass, consequently there is no requirement for an external by-pass, however the design of the system should be such that it prevents boiler § ‘cycling’.

jimjimt

Good man you are making the right decision long term.

Now that you are doing it by the book you should note that it is illegal for anyone to work on a gas boiler unless they are RGII registered.