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Discuss Simple relay for secondary pump circuit in the Central Heating Systems area at ElectriciansForums.net

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I am looking for guidance on adding a second pump for the underfloor section of my central heating. I am using a blending valve for the UFH supply by teeing off the main boiler feed into the 3 way valve and then to the pump and UF circuit valves (2).
I am ok with the wiring I simply need a relay to switch the UFH pump (and boiler) using the orange switched live from the valve via room programmer to avoid both pumps running when the UF only is required.
I need a 240v relay with say 10 amp capacity. I will put in an enclosure (I need one for each valve on the UFH circuits) so spade connections. I am having trouble finding something suitable in Farnell etc. Anyone know what I need and where to source please?
The boiler is a simple rocket oil fired boiler so no PCB controls.
Cheers
 
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SparkyChick

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Depending on exact switching configuration, you may be better with a DIN rail mounting socket and a plug in relay... or a contactor suitable for a consumer unit.
 
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  • #4
Thanks but I saw these and it is overkill for one pump circuit. I just need something in an enclosure next to the heating system wiring centre. It only has to switch a 25 watt pump at 240v when the motorised valve calls for heat.
 
No worries, I thought you were struggling with the required current rating, at 25 watts you will have no prob finding suitable device
 

davesparks

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Normally you would have both pumps running for underfloor operation, not just the underfloor pump. Usually the underfloor pump only circulates the water around the underfloor pipework after the blending valve, the boiler circulating pump delivers the heat to the underfloor manifold.
Running the boiler without the circulating pump may not give the boiler the required flow for correct operation.
However you do need to prevent the underfloor heating pump from running when only the regular heating is required.
 

davesparks

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As for where to get a relay, just go in to your electrical wholesalers and ask for an 8pin relay with a base and suitable enclosure.
 
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  • #9
Thanks guys. By way of explanation the pumps are in parallel therefore running either one is pulling directly off the boiler flow so you do not need to run both. Most diagrams show the UFH pump in series which means you are trying to pull flow though the main boiler pump or have both running and try to balance them. Mine pumps from the boiler flow directly into the blending valve and the UFH pump is pulling through that valve to the loops. The returns are common with a feed back to blending valve cool inlet (RAV-K and VMV)
I will go and fetch a couple of the relays as suggested.
 
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  • #10
Relays installed and I can get pumps to run independant but the boiler is still back feeding the relays. Boiler is on its own terminal with connections to each relay. One zone calls and relay energises pump and boiler fires up. Then zone UFH calls and pump 2 starts. All good. BUT when either zone switches off both the relays remain energised unless I pull the boiler feed off that relay and then one clicks off. I tried all ways of connecting boiler feeds but they always provide a reverse feed through the relays.
Any ideas?
 

Leesparkykent

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Relays installed and I can get pumps to run independant but the boiler is still back feeding the relays. Boiler is on its own terminal with connections to each relay. One zone calls and relay energises pump and boiler fires up. Then zone UFH calls and pump 2 starts. All good. BUT when either zone switches off both the relays remain energised unless I pull the boiler feed off that relay and then one clicks off. I tried all ways of connecting boiler feeds but they always provide a reverse feed through the relays.
Any ideas?
How have you connected it? Can you show a diagram?
 
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  • #12
I think I just cracked it! I will do a diagram and publish in case anyone else needs to do this. Just monitoring at the moment.
Thanks
 

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