Adding a cylinder thermostat

[+Sid]

Hello
My new house to be has a conventional domestic heating system with a gas fired boiler for heating the radiators and water in a storage cylinder. It's all controlled from a Hive controller that is fitted to a wall in the hall.

The current owner has the hot water to come on for an hour in the morning and an hour in the evening. He sets the room temperature to 18 degrees but is he able to control the temperature of the hot water accurately without a cylinder thermostat?

Presumably, there is a thermostat for the hot water temperature on the boiler that can be set but is this good enough and what would be involved in fitting a thermostat to the hot water cylinder?
bloody hell! what kind of captcha is that

 

[Richard-the-Ninth]

is he able to control the temperature of the hot water accurately without a cylinder thermostat?

My understanding is no. (How will it know what the temperature of the cylinder is)

In the UK if you have "an airing cupboard" you should have either an S plan system or a Y plan system.

As I understand it one will have a Y (electric) valve and the other will have 2 single (electric) open or closed valves

With the Y valve hot water comes in at the bottom and goes left, right or both. (For arguments sake, left is heating, right is for hot water)

With 2 single valves, it is one for heating, one for hot water.

The boiler will always heat water until it is told not to, be that by an external stat or its own internal stat.

I may be in error, so I suggest you search for S plan and Y plan heating system

 

[SPECIAL LOCATION]

I also may be wrong.. (and sharing the semi-ignorance-boat with Sir-Richard)..

But I have seen some old, non-standard, limited functionality heating systems..
e.g. no motorised valves OR a pump!! Gravity fed, using hot water rises principal...
Basically if the boiler is on... It heats everything, radiators & hot water cylinder..

And the only control is if the boiler gets too hot and it turns itself off..
Or the radiators are manually or thermostatically adjusted!

A bit more thorough investigation and identifying exactly what you have, is needed.

 

[Andy™]

pure gravity won't work for heating since the downstairs radiators & pipework will be lower than the boiler.

gravity HW and pumped heating was common though, if you want hot water it only switches on boiler. if you want heating & hot water its pump & boiler. can't have heating without hot water

solid fuel boilers do need gravity hot water or radiator to allow heat somewhere to go if the pumps fails

 

[binky]

I believe the boiler monitors the water temperature of water coming back to the boiler from the tank. So if water is already hot, it stops heating the water, albeit the pump may still be running for the full hour.

 

[Geoff1946]

Agree you need to work out what you have. Trace the pipes.
If two largish pipes go directly from the boiler to the HW cylinder then it's an old gravity system.
Where is the pump ? On fully pumped systems it's often (though not always) integral to the boiler, but on gravity HW systems it will be separate, either adjacent to the boiler, or quite possibly under the floor.
Are there any motorised valves ? The most basic old (gravity) systems have none.

 

[+Sid]

Thanks for all your replies. When I move in I'll have a closer look at what there is in light of all of your comments

 

[Xannan]

Yeah, having a thermostat directly on the hot water cylinder can give you more precise control over its temperature. It ensures you're not heating water unnecessarily.

 

[kerching]

If you have a Y plan ( work of the ) then your cylinder stat will need a 3 core and earth as a DHW off signal is needed to save the valve going all moody

 

[Dricah]

Yep, the boiler should have its own thermostat to control the hot water temperature, but getting a cylinder thermostat will give you way better control. When I moved into my house, I had a similar setup and adding the cylinder thermostat made a big difference in managing the hot water and cutting down on energy use.

I got a professional to install it—it wasn't a huge job. They just attached the thermostat to the cylinder and wired it up.

 

[+Sid]

if you have a Y plan ( work of the ) then your cylinder stat will need a 3 core and earth

I've been looking at how to wire one of these. If the stat is double insulated like the DRAYTON HTS3 CYLINDER STAT (95630) could I use twin & earth to wire it, and is +/- 8K tolerance like the HTS3 acceptable?

 

[kerching]

No. It needs 3 core and earth ( even if the earth isn’t used ) if it’s a Y valve
Common
DHW ON
DHW Off

 

[Richard-the-Ninth]

just saying...........

Even the stat instructions say it requires 3 wires for installation


Buy some 4 core flex while you are at screwfix Click here

Also

your cylinder stat will need a 3 core and earth as a DHW off signal is needed to save the valve going all moody

 

[Andy™]

if its Y plan... C/S plan would only need 2 core... but we don't know what he's got

 

[+Sid]

OK Thanks for that. I'll wait to see exactly what I've got.

 

[+Sid]

What I was really asking was if the stat was double insulated would it require an earth and could the earth wire in twin and earth cable be marked up as live and used?

 

[Andy™]

What I was really asking was if the stat was double insulated would it require an earth and could the earth wire in twin and earth cable be marked up as live and used?

if you think using a cpc as a line conductor is acceptable, you need to stay away from electrics and get someone competant to do the job for you

 

[+Sid]

That's why I was asking

 

[+Sid]

I only ask because I have seen gas engineers do it when they wire the sender to the boiler for wireless programmable room stats

 

[Geoff1946]

The moral to that is don't learn your electrical practices from a gas engineer. It really is bad practice which could potentially kill a person misunderstanding the cable useage in the future.