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Central Heating Relay help needed

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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)
 
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thanks for the reply. There is no zone valves. It is not S or Y plan???
so does the boiler heat the hot water via a flow switch internally within the boiler? As it was on a programmer before. The boiler didnt have a permanent live. Only had 2 x switched lives (1 from CH channel & 1 from HW channel)
 
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Elrick said:
Hi

What your trying to do wont work as the hot water will still come on as it is gravity no zone valves to stop flow of water to cylinder
Click to expand...

I see what you mean, I know its gravity fed etc. Does this system heat the water continuosly when its used? As the boiler didnt have a permanent live. The HW was switched from the HW channel on programmer. I dont fully understand the system as I am only 25 and this system hasnt been used for a few years ha
 
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You're right, you will need a relay to run the boiler when the pump is on. I have the same type of system. This relay and base will do the job, fitted into a suitable adaptable box.

230v AC 8 Pin Relay 2 Pole

Here's a similar relay and base used for interfacing a frostat to a heating system.

[ElectriciansForums.net] Central Heating Relay help needed

Yes, the hot water will be heated when the CH is on, but it's no worse than before, so not a problem.
 
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jaydee81 said:
what you need to find is a c plan diagram will all become clear
Click to expand...

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?
 
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HandySparks said:
You're right, you will need a relay to run the boiler when the pump is on. I have the same type of system. This relay and base will do the job, fitted into a suitable adaptable box.

230v AC 8 Pin Relay 2 Pole

Here's a similar relay and base used for interfacing a frostat to a heating system.

View attachment 17066

Yes, the hot water will be heated when the CH is on, but it's no worse than before, so not a problem.
Click to expand...

thats great thats what i was looking for . I dont think everyone understood. So doing this will mean i can use the central heating (but at the same time it will heat the water) and i can also use the hot water on its own and this will not run the central heating pump??
 
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jaydee81 said:
would heat through programmer or when heating is on as you cant seperate the two would be considering making it a fully pumped system if me would save customer a fortune on heating bill
Click to expand...

i understand now thanks. the customer is selling the house so all costs to a minimum. I will just install relay and explain the situation. thanks for your help
 
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connectrix said:
thats great thats what i was looking for . I dont think everyone understood. So doing this will mean i can use the central heating (but at the same time it will heat the water) and i can also use the hot water on its own and this will not run the central heating pump??
Click to expand...

Yes, this should work fine. You can also get programmers (or could) which have a switch on the back which you set on installation. This determines whether the HW output comes on automaticcally with the CH output (for older gravity HW systems as you describe).

Ideally you would add a cylinder stat to inhibit the boiler when HW only is on and the cylinder is up to temperature. Of course, going fully pumped would be the ideal solution.
 
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connectrix said:
thats great thats what i was looking for . I dont think everyone understood. So doing this will mean i can use the central heating (but at the same time it will heat the water) and i can also use the hot water on its own and this will not run the central heating pump??
Click to expand...

So is there any point in this as with the time clock calling for heating & hot water you get both and if it's calling for heating you get both.
 
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Elrick said:
So is there any point in this as with the time clock calling for heating & hot water you get both and if it's calling for heating you get both.
Click to expand...

I suppose it just means that you can heat the water without running the central heating. If its the middle of summer and you don't want the heating on you can still heat the water. As there is no trv s on the rads
 
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