Dual Cylinder Thermostat

[proppi]

Hi,

Trying to understand how the (dual?) thermostat on my freshly installed indirect unvented cylinder (manufacturer is Joule) is supposed to be working. The thermostat is attached about a third from the bottom and let's me set the temperature between 25 and 65 degrees. It has been wired to the immersion heater, ie as long as I don't use the immersion heater (most of the time) it will be useless and the flow temperature of the boiler will control the temperature of the hot water which is not very practical (I might want a very high flow temperature if it is very cold outside but keep hot water at say 60 degrees). If I ask the installer to come back and wire the thermostat to the motorised valve of the boiler instead than this should solve this issue, but then I would not have any thermostat that would help to prevent overheating if I ever use the immersion heater.

How is this supposed to be done properly? Do I need two thermostats, one controlling the immersion heater and one controlling the motorised valve of the boiler? Or can my existing thermostat be wired to both?

Would appreciate any advice on this!

 

[Stanios]

You have been misinformed by the looks of it. Its called dual because it is a thermal cut out and a thermostat not because it does immersion heater and coil. God forbid you can see the immersion heater stat
The thermostat on your cylinder will control the boiler and the motorized valve. Just turn it up and down and hear the boiler come on and off after a little delay. Somewhat dubious about your installer who was unable to explain such a basic thing

 

[proppi]

Thanks Stanios for the explanation - indeed I misinterpreted what 'dual' means.

So the immersion heater does have a stat that I cannot see but which prevents the cylinder from overheating?

Regarding the thermostat that I can see: Unfortunately the installer did wire it to the immersion heater and not the motorized valve. I am sure about this, firstly because I can see the wires and secondly because the installer stated it claiming that I could use the flow temperature of the boiler to control the hot water temperature. So this is a wrong installation then?

 

[Stanios]

Thanks Stanios for the explanation - indeed I misinterpreted what 'dual' means.

So the immersion heater does have a stat that I cannot see but which prevents the cylinder from overheating?

Regarding the thermostat that I can see: Unfortunately the installer did wire it to the immersion heater and not the motorized valve. I am sure about this, firstly because I can see the wires and secondly because the installer stated it claiming that I could use the flow temperature of the boiler to control the hot water temperature. So this is a wrong installation then?

For your own safety I hope this isn't true. Boiler flow can go above 80c which when transfered to the cylinder and in turn your tap can instantly cause serious burns to your skin. The cylinder stat must communicate with the boiler, if it has wire coming out of it like you say then that wire must go to the wiring centre where it is wired to the motorised valve. I've never seen a cylinder stat wired to immersion heater this sounds very dodgy / dangerous
Either post a photo here of your cylinder and immersion or get a G3 qualified plumber in.

 

[kris]

Hi proppi , like stanios said if you could let us see some pics so we can advise you properly just incase your mixed up, cheers

 

[proppi]

Thanks to both of you. Pictures below. The black cable runs from the thermostat to the grey box, one white cable runs from the grey box to a switch at the wall which allows to turn the immersion heater on/off, the other white cable runs from the grey box

to the immersion heater.

Could the boiler heat the water so much that the pressure relief valve will open (asking this as we had hot water running through the tundish the other day - at this time I believe we were unknowingly using immersion heater and boiler to simultaneously heat the hot water)?

 

[Stanios]

That's totally wrong, and just straight out dangerous. Not following manufacturer's instructions, contravenes Unvented regs and pretty sure contravenes any relevant wiring regulations as the immersion heater can only be wired straight into a dedicated fuse spur with its own dedicated fuse/mcb on your fuse board.

I fear the immersion heater stat is either missing or faulty and your "installer" has decided to wire up the cylinder stat directly to the immersion. I can applaud the creative thinking but this is just bonkers and again dangerous.

Turn your system off, get a G3/unvented qualified plumber asap and ask him to rewire and recommission this whole thing.

 

[proppi]

Many thanks again, Stanios, very clear.

My only issue is that the installation of the cylinder (and a new Vaillant ecotec plus system boiler) was done as part of a refurbishment project for which I have a contract with a main contractor so I will have to go through him to avoid any problem with his warranty.

Can I just check one more thing please: Am I supposed to get a certificate following the installation of the cylinder? I have received a gas safe certificate for the installation of the boiler but no specific certificate for the cylinder (or would this be automatically included in a gas safe certificate for a system boiler)?

Many thanks again for your help on this. Much appreciated.

 

[Stanios]

No, certification of cylinder isnt mandatory they can self certify to show they have unvented qualification which this guy clearly hasnt got

 

[student plumber]

No, certification of cylinder isnt mandatory they can self certify to show they have unvented qualification which this guy clearly hasnt got

I thought even if you self certify you still have to give the customer a certificate to say it's fitted properly; or am I thinking about a Benchmark certificate, or are they the same thing.

Just to be clear I do not install unvented as I am not qualified .

 

[Chuck]

At the end of this sort of job a qualified installer would normally complete the manufacturer's Benchmark checklist, which is left with the customer along with user instructions. Also, within a specified number of working days, they must issue a Building Regulations Compliance (BRC) certificate and have this transmitted to the local authority's building control dept.

I am not a lawyer, but I believe that it's Building Regs notification that is the legal requirement. Competent-persons scheme membership allows building control to accept the BRC instead of insisting on the full approval process (design, supervision and inspection of the work).

Benchmark is an industry scheme for promoting good practice accross the heating and hotwater sector. Not, AFAIK, a legal requirement but useful for providing evidence that legal requirements have been complied with.

Building Regs:

Building regulations approval - GOV.UK

Benchmark Scheme:

Heating and Hotwater Industry Council » Benchmark for consumers

 

[Chuck]

I have received a gas safe certificate for the installation of the boiler but no specific certificate for the cylinder (or would this be automatically included in a gas safe certificate for a system boiler)?.

If "Install an unvented hot water vessel" is not explicitly specified on the certificate then it isn't covered by the certificate.

From what I can see on the photos you aren't going to get a certificate until it's redone by someone who is G3 qualified.