Cylinder thermostat wiring question

[padstar]

The plumber has temporarily wired up my central heating system to give me hot water and heating. He has wired an S-Plan system as requested but i have noticed he hasn't ran the hot water via the cylinder thermostat so at the moment the boiler heats the water I the cylinder when the programmer tells it to but doesn't stop when it hits the set temp. I have set the programmer to heat water for 1hr in the morning and evening for the time being but i want to run via the stat to prevent potential for overheating and for it to be connected correctly.

The cylinder has 6 electrical terminals. The 3 on the right are L/N/E. I assume I connect the emersion heater supply here so that if the boiler ever goes down i can flick the water heater switch and heat via the immersion? Is this correct?

On the left there are 3 more terminals labelled 1/2/3. I assume the 2 port valve signal cable goes into one of these and then a cable out back to the control box essentially breaking the heat water command to loop in the cylinder thermostat. Which terminal (1/2/3) is for signal in and which for signal out?

Many thanks in advance

 

[flameport]

1&2 for S plan, with 1 as the input and 2 as the switched output, although it doesn't really matter with only 2 as it's just connecting them together when heat is required.
3 is only used for Y plan which requires a 'hw off' connection.

LNE for the immersion heater, normally supplied via a 16A circuit and a 20A isolator switch. Not a FCU with a fuse in it.

Wiring info can also be found in the instruction leaflet on the floor.

he hasn't ran the hot water via the cylinder thermostat

The 'plumber' is an idiot.

 

[padstar]

Thanks Flameport. So just loop the stat in between the 2 port valve and control centre via terminal 1 and 2.

I got a 16A circuit for the immersion linked water heater switch on the landing then to a fused spur which i had planned to connect the immersion to. So does this need changing to a 20A isolator?

 

[Madrab]

I am really sorry to say this @padstar but you need to stop heating the cylinder via the boiler, if he hasn't wired it into the stat.

You should not heat an unvented HW cylinder without a thermostatic control, that's could be downright dangerous. That plumber needs a serious kick in the stones to leave an unvented HW system like that, even temporarily. It would have only taken another 5 mins to run a suitable temp cable to tie the stat into the system.

Unvented cylinders are not DIY'able, any trade working on it needs to be qualified to work with unvented cylinders for your safety.

 

[ianmcd]

As @Madrab says , it is not that simple with an unvented cylinder, the zone valve is also a safety device and definately not a DIY job

 

[Tetrarch]

I am really sorry to say this @padstar but you need to stop heating the cylinder via the boiler, if he hasn't wired it into the stat.

You should not heat an unvented HW cylinder without a thermostatic control, that's could be downright dangerous. That plumber needs a serious kick in the stones to leave an unvented HW system like that, even temporarily. It would have only taken another 5 mins to run a suitable temp cable to tie the stat into the system.

Unvented cylinders are not DIY'able, any trade working on it needs to be qualified to work with unvented cylinders for your safety.

Apologies in advance for this...

I'm in a similar situation. I have a Pellet Boiler + UFH + Rads with HIVE installed by Pellet Boiler Installers a year ago. This was no problem for them but when I had my 300L Megaflo installed in the summer the wiring scared the plumbers (whose "wet work" was faultless IMO). They were very accomodating and stuck to a fixed price quote for the tank install.

This is where I am going to get roasted....here goes...

I have wired the HW diverter Motorised Valve direct into a Smart Socket that means that when it is opened and heating somewhere else is on, then the tank warms up. There is NO immersion connection.

The water is never on for more than an hour at a time (always set manually - never timer only) and my theory was that the Boiler Max Temperature setting (65 degrees) would perform the same function as the Megaflo themostatic control.

Are you saying that what I have done is sub-optimal or downright dangerous? My setup is just a temporary HW add-on until everything gets ripped out and replumbed if and when planning comes through

Regards and neck extended for the axe

Tet

 

[Madrab]

The cylinder thermostat should be the primary control/cutoff for any HW cylinder be it vented on unvented. It just more important for an unvented as these can potentially be dangerous/explosive.

Any of the safety controls on an unvented should engage automatically and not have to have any manual intervention, us humans are seriously fallible and can forget things or change things when we shouldn't. The problem with letting the boiler flow manage the temp control is if, for whatever reason, the boiler goes into a runaway condition and starts to increase the flow temps and doesn't stop there is then nothing that will automatically stop the flow to the cylinder and stop it from overheating.

Don't get me wrong, an unvented cylinder does have multiple safety features that activate if things get to hot or it over pressurises but there are multiple fail safes on these cylinders for a reason and none should be omitted.

When you say the valve is connected to a smart socket, what controls the smart socket and does the valve then control the boiler?

 

[Tetrarch]

When you say the valve is connected to a smart socket, what controls the smart socket and does the valve then control the boiler?

I have wired my Honeywell MV into a BG Smart Socket.

British General 800 Series 13A 2-Gang SP Switched Smart Socket White - Screwfix

Order online at Screwfix.com. Control and schedule power in the home or outside via touch, voice commands or app. No need for a hub, cloud costs or subscription. Quick and easy set-up, with in-App support. Set timer schedules, countdown function or random security options. Compatible with Google...

www.screwfix.com

I operate this from my phone manually or via Alexa, but it has a safety override feature that limits the run time for a socket "On" condition to a user-definable period. I have set this to one hour to avoid fleshware issues.

The boiler controls are completely separate and the boiler only fires up when either the UFH or the Hive call for heat.

Regards

Tet

 

[flameport]

I have wired my Honeywell MV into a BG Smart Socket.

If the valve is directly connected to that and not via the cylinder thermostat, you can't use it. There is nothing to stop the cylinder being heated for ever.

If that supply from that socket goes via the cylinder thermostat and then to the valve then it can be used, although it's still a fairly useless way to do it.

 

[Tetrarch]

Thanks for taking the trouble to reply.

The reason for the setup is that I'm trying to achieve a particular outcome that means I need to operate my HW outside of my HIVE ecosystem.

My pellet boiler is great, but the pump is noisy and has a long overrun. My plan is that I'm trying to find a way to dump the Primary Circuit into the cold water of the HW tank to a) Shut down the primary circuit more swiftly and b) Dump what is excess heat usefully into the Megaflo

My thought is that all I need is a timed power source (i.e. the Smart Socket), plus the motorised valve and the tank thermostat. This can then be synchronised with the Hive heating schedule to effectively separate the HW circuit from the rest of the heating.

I too, just need the correct wiring to bring the cylinder thermostat wires into the equation for the safety reasons you point out.

Regards

Tet

 

[Madrab]

Thinking it through and with a bit of a hybrid setup then ... You could possibly set up a bypass with another 2 port to allow the over run to bypass the main 2 port and allow it to flow to the cylinder. That way the cylinder stat and main 2 port would still control the boiler with a standard wiring setup, keeping that safety system intact, but the other path will allow the pump over run to still flow through the cylinder.

That 2 port could then be timed to open via your smart control only when the call to the boiler for CH/HW is shutoff but the pump is in over run mode.

 

[Tetrarch]

Hi Rob,

I was trying to avoid having another bypass. Trying to find a single solution for a two-season setup

Summer - Turn Hive Master Themostat on (to call for heat from the boiler) with all rads off and HW motorised valve (HWMV) on the same schedule

Winter - As described above. The main limitation being that the heating has to be on for any HW to be generated


Effectively the HWMV is contolled totally inependently of the heating system. Would this mean that I don't need an additional bypass and MV

Regards

Tet

 

[Madrab]

You approach above wouldn't mean the MV is independently controlled, it would be controlled by the Hive through the cylinder stat as any normal system?

The issue with an unvented is it must have an automated shut down when it reaches temp, the cylinder stat must be able to shut off the heat source to the cylinder, that would normally be by the stat closing the MV and that shuts down the heat source. They should not be managed by an independent control that isn't part of the system interlock.

From what you said before you wanted to be able to channel the boiler overrun into the cylinder, keeping the standard automated interlock in place, then that would normally be managed with a bypass. I take it your cylinder has one coil not 2?