Central Heating Relay help needed

[connectrix]

I have an old E type boiler that has a gravity fed water system , heated by the boiler then stored in a tank. The central heating just has a pump. I have removed the old room stat and programmer and installed a new 2 channel programmer and room stat.
I thought it was all wired correctly as it has been that way for years but when connecting the new programmer etc up I can see a problem. Basically you can heat the water on its own fine but if you want the central heating on you have to have the water on at the same time to fire the boiler. So you cannot just have the central heating on its own as only the pump runs but the boiler is not firing. From what I can see the only thing to do is link the central heating pump to the boiler suppressor so they work together when the room stat requires heat. However this will mean that if you only want hot water then the central heating pump will start running so I was thinking of installing a contactor/relay (feeding the coil from the room stat) so that the boiler will fire when the central heating pump is running and the hot water will work fine without running the central heating pump??
Can someone please confirm this is correct and advise me of the best contactor/relay to use and where to buy as I has a look in the RS catalogue and there are various types etc...
Obviously I know I need a 230v coil and probably din mounted with screws. I am familiar with contactors but not used relays before (I know they use the same principal)

 

[guest119]

You need an old 10/16 programmer.
10 for gravity HW and pumped heating via room stat.
16 for fully pumped.
With the 10 prog setting the slider for heating dragged the HW one with it and the HW slider would work on its own.
With the 16 prog setting the sliders were independent as they each controlled a zone valve (fully pumped system)

Boydy

 

[Megavolt]

You are missing the point gravity hot water means gravity you do not use the pump to get hot water. You turn the boiler on that in turn heats the hot water that travels to the cylinder by gravity. There is no need for a relay or any of this.

 

[guest119]

If you use one channel of your 2 channel device for hot water (just to fire the boiler) and the second to feed the thermostat (and to the pump) then set the times so the 2nd channel is never on when the 1st isnt.

Boydy

 

[guest119]

Thanks Ive just looked at a C plan diagram. This makes sense, however on the system I am working on there is no cylinder stat or zone valve present. Is this wrong? Will my theory not work? I just need to understand the hot water. Does it re heat as its used or do you heat the tank for timed periods via the programmer?

If not used, the hot water temp is controlled by the boiler stat.
Therefor HW tank and boiler end up same temp.

Boydy

 

[connectrix]

That's what I have dun so far. He channel just turns the boiler on and it does its own thing then ch channel goes to room stat then to pump. If the hw is off am I just pumping cold water? Surely the boiler needs to be fired at the same time as the pump to heat the rads? This is why I wanted to fit a relay in between the ch pump and the boiler so that the boiler would fire with the pump but u can also run the hw without the ch automatically pumping as the coil is fed from the doom stat?

 

[connectrix]

Stupid I phone I meant hw channel at top and room stat at bottom

 

[connectrix]

You are missing the point gravity hot water means gravity you do not use the pump to get hot water. You turn the boiler on that in turn heats the hot water that travels to the cylinder by gravity. There is no need for a relay or any of this.

i understand that the water will automatically heat as soon as the boiler is fired. so how does the boiler heat the central heating fluid then?

 

[guest119]

Right, with what you have got fitted.
channel one, perm live feed, switchwire out to boiler.
channel two, not a perm feed but a loop from channel one boiler supply.
Then channel 2 can switch all it likes but without channel one energised you dont pump cold water.
phew!


Boydy

 

[connectrix]

Right, with what you have got fitted.
channel one, perm live feed, switchwire out to boiler.
channel two, not a perm feed but a loop from channel one boiler supply.
Then channel 2 can switch all it likes but without channel one energised you dont pump cold water.
phew!

that means you cant have the central heating on without the hot water being on. If you do it my way you can turn the heating as normal (i know it will automatically heat the water) and you can also turn the hot water on , on its own without turning the central heating on?

 

[guest119]

No different to my suggestion Conne.
The only quick and cheapest way forward is to fit a zone valve to the top cylinder coil connection allied to a strap on stat.
Then the hot water wont try to achieve the same temp as the boiler, and...... you can have genuine heating only.

Boydy

 

[ayjay]

once the boiler is on, the hot water will gravitate around the coil in the cylinder by gravity theres zilch you can do about it, hot water cant be separated from the radiators end of
all a programmer can do is turn on the pump
+boiler
the feed pipes from the boiler to the cylinder coil are normally 32mm and are separately connected to the rear of said boiler theres no way of controlling the gravity flow to the coil

 

[ayjay]

No different to my suggestion Conne.
The only quick and cheapest way forward is to fit a zone valve to the top cylinder coil connection allied to a strap on stat.
Then the hot water wont try to achieve the same temp as the boiler, and...... you can have genuine heating only.

Boydy

the open expansion pipe that goes up into the expansion tank may become compromised by doing that !!!

 

[guest119]

once the boiler is on, the hot water will gravitate around the coil in the cylinder by gravity theres zilch you can do about it, hot water cant be separated from the radiators end of
all a programmer can do is turn on the pump
+boiler
the feed pipes from the boiler to the cylinder coil are normally 32mm and are separately connected to the rear of said boiler theres no way of controlling the gravity flow to the coil

Not true Ayjay, zone valve will kill gravity flow at top coil connection, not blocking off vent pipe.

Boydy

 

[connectrix]

How does the boiler heat the rads?

 

[ayjay]

i guess u might be right bouydy i trying to think how i did it on my old system--

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How does the boiler heat the rads?

by gas and a pump