Megaflo and Honeywell Valve Wiring

[Tetrarch]

Hi I'd like to run my Megaflo independently from the rest of my heating set-up

Cylinder - Heatrae Sadia Megaflo Eco 300i Indirect Unvented Hot Water Cylinder - 95050475
Motorised Valve - Honeywell Home 272828

What I would like to do is wire up the valve such that the valve opens when the power is on (by a smart timed plug), but to close when the temperature setting on the Megaflo is reached. Thus I only have a wired plug and the cylinder to connect together.

There is no requirement for the boiler to be triggered as this will be controlled independently, I am not intending to install any immersion wiring at present

Regards

Tet

 

[CBW]

Is it the boiler that heats the unvented cylinder? I’m not entirely sure what you’re asking is possible as there‘s certain safety criteria that needs to be met with unvented cylinders.

 

[Tetrarch]

Is it the boiler that heats the unvented cylinder? I’m not entirely sure what you’re asking is possible as there‘s certain safety criteria that needs to be met with unvented cylinders.

Yes - I have a Windhager Pellet Boiler with Heatmiser-controlled UFH and Hive-controlled Rads upstairs. The Pellet Boiler has an overrun and PR controls built-in. I had the wet side of the Megaflo installed professionally, but the smart stuff wasn't ready to enable an electrical connection to be made.

All I am trying to do is divert already hot water in the primary circuit into the Megaflo, but to ensure that the tank Thermostat stops the flow of water when it reaches the appropriate temperature. The Windhager has its own primary circuit temperature and pressure management capabilities.

I'm effectively trying to make the Megaflo act as an extra "manually" controlled radiator that only works when the heating circuit is on. During the winter the tank will heat up when the rads are on and during the summer all the rads will be off but the main Tstat will be set to come on at the same timings as the Honeywell valve

As a bonus I can use this functionality to dump heat that would otherwise be wasted into the cylinder when the boiler is in its cooldown cycle during the winter. I've already cleared this approach with Windhager

Tet

 

[ianmcd]

What you want to achieve is easily enough done , but you cant wire this yourself, The zone valve needs to be wired by someone G3 qualified as the zone valve must also become an over heat protection and be wired accordingly

 

[Tetrarch]

I'm a little confused. The primary circuit from the boiler is capped by the boiler itself at 70-deg. Does this not protect the Megaflo against overheating?

I want the MV to be open by timer and closed by the Megaflo thermostat. This is only a temporary arrangement as the whole heating will be uprooted when our planned building work starts.

Regards

Tet

 

[ianmcd]

I'm a little confused.

That is why it requires a G3 qualified engineer to wire it correctly

 

[Tetrarch]

That is a little condescending, but I appreciate you taking the time to reply.

Is what I want proscribed or is it just tricky to connect?

Theoretically, I believe that to get the functionality I want, the Megaflo and the MV perform exactly the same function as a Rad and a TRV. I do not need a G3 qualified engineer to install one of those.

At the moment I could achieve the result I want by turning on the house Thermostat and opening the valve manually for a period of time. I can also achieve this by just connecting the MV to the mains on a timer. What I am trying to do is IMPROVE safety by employing the Megaflo Thermostatic control to stop the flow to the MF when the desired temperature is reached - hence reaching out to the denizens of this forum for help

Regards

Tet

 

[stem]

Theoretically, I believe that to get the functionality I want, the Megaflo and the MV perform exactly the same function as a Rad and a TRV. I do not need a G3 qualified engineer to install one of those.

That is correct, you don't. However the G3 qualification is in relation to the unvented hot water cylinder and not the rest of the central heating system.

Unfortunately, (or fortunately, depending upon how you look at it ) that's the way it is. I am a qualified electrical engineer and have also helped plumber friends and family, as well as many on this forum with troubleshooting heating controls, and I understand unvented hot water systems work. However, I don't have a G3 qualification and as this is required by the building regulations to work on unvented systems I have to draw the line when it comes to working on them and leave it to those that do.

You can find more details about the G3 requirements on the Megaflo website under the 'unvented systems' heading.

 

[ianmcd]

That is a little condescending, but I appreciate you taking the time to reply.

Is what I want proscribed or is it just tricky to connect?

Theoretically, I believe that to get the functionality I want, the Megaflo and the MV perform exactly the same function as a Rad and a TRV. I do not need a G3 qualified engineer to install one of those.

At the moment I could achieve the result I want by turning on the house Thermostat and opening the valve manually for a period of time. I can also achieve this by just connecting the MV to the mains on a timer. What I am trying to do is IMPROVE safety by employing the Megaflo Thermostatic control to stop the flow to the MF when the desired temperature is reached - hence reaching out to the denizens of this forum for help

Regards

Tet

Not condascending in anyway, you can not just add a zone valve to an unvented HW system and wire it like "a rad and TRV" it is a safety device and has to be wired as such, not my opinion , it is there for very good reason, but as you are now an expert (now that IS condascending) what could possibly go wrong

 

[Mister Banks]

Not condascending in anyway, you can not just add a zone valve to an unvented HW system and wire it like "a rad and TRV" it is a safety device and has to be wired as such, not my opinion , it is there for very good reason, but as you are now an expert (now that IS condascending) what could possibly go wrong

If that doesn’t make the OP think twice then nothing will!

 

[Tetrarch]

OK - I give in

I don't want to waste a G3-qualified plumber's time quoting for something that cannot be done.

What is the best way for me to specify the job in order to give as much necessary info as possible?

Regards

Tet

 

[Agile]

The whole point of the G3 qualification is to ensure that the unvented cylinder will have the heat source disconnected by a spring return valve when it has reached the selected heated temperature.

So that immediately power is removed from the heating motor valve it will close mechanically and remove power from the call for heat.

I seem to recall there is an additional requirement when heated by burning wood or pellets because they usually cannot be turned off immediately like gas or oil.

 

[Tetrarch]

The whole point of the G3 qualification is to ensure that the unvented cylinder will have the heat source disconnected by a spring return valve when it has reached the selected heated temperature.

So that immediately power is removed from the heating motor valve it will close mechanically and remove power from the call for heat.

I seem to recall there is an additional requirement when heated by burning wood or pellets because they usually cannot be turned off immediately like gas or oil.

Thank you That makes a huge amount of sense - turning the call for heat off is a better solution than the idea that I had. I don't need or want there to be any call for heat when the valve is activated but a command to turn off the heat would be excellent.

The Pellet Boiler is set to 70-deg and has quite a sophiticates temeperature management protocol for both heating and cooling cycles. I assume that I should specify the set-up when asking for a quote

Regards

Tet

 

[Agile]

Yes, it is essential that you give the full details of your installation.

No one has commented on my suggestion that there are additional requirements when wood or pellet burners are used as a heat source.

But I do not usually think of those kind of things unless something has prompted me to do so.