Where and which relays to buy

[elsmandino]

Hi there.

I need to buy a couple of relays to update my heating system:

* A mechanical SPDT NO relay, 230v 10A
* A mechanical SPST relay, 230v 10A

If I type these into Google, I get a whole range of different makes from all sorts of sources.

What brands should I look for and are there any reputable sellers that I should use to guarantee a genuine product?

Prices seem to be about £10.00 each - more than I was expecting. Is that about right?

 

[jj4091]

It's pretty much a case of a relay is a relay and if it's only for your heating controls then I doubt it will be carrying much load. So just take your pick.Get one to suit your existing base.

 

[davelx]

And note that functionally, DPDT relays will meet both your requirements. Just don't connect the contacts you don't need.

 

[Gasguru]

If you're going to do the job properly you should use a plug in relay (for easy replacement) and ensure the contacts are either Silver Tin Oxide AgSnO2 or the newer Silver Tin Indium Oxide (often shown as AgSnIn).

Although controlled and limited, modern pump and boiler circuit boards can have substantial inrush currents that can weld traditional contacts.
15 years ago Grundfos caused a massive scandal when they launched their new pumps without considering the inrush currents pulled when energised, resulting in fried relays in heating programmers and boilers.

Stick to known brands eg. Omron, Finder etc. no ebay junk with fake specs.

 

[ericmark]

Main problem is most relays are designed to go into an enclosure, I have a relay with my central heating, and the oct base clips onto din rail in a box and the relay pokes out of a hole in the box top so can be changed without opening the box, it was selected as I had the relays in stock and the box in stock, and reason for them is I have two pumps and one boiler, and the motorised valves only have one micro-switch built in.

Control boxes like this

have relays built in, OK the 4 channel version is £70, but no need for extras, mine look like this

at £8 each seems cheaper, but box like this

is another £10 so total still nearly £30. A smart plug in socket can often work out cheaper, simply as so many sold.

So tell us your aims. My central heating was a mess, now much better, but I made errors on the way, looking back I can see my mistakes, not all my fault, products did not do what they said they would do. Nest Gen 3 was a big error, it did not do as it said on the box.

I do not really need two pumps, they were here when I bought the house, I got two motorised valves to stop the pumps forcing the water around the system backwards when only one in use, would have been better to have just used electronic TRV heads on all radiators. But hindsight is easy.

Also consider when you get older, will someone else be able to repair what you have? I did consider using a PLC (programmable logic controller) I had two spare in my junk box, and I had the software to program them. But once I can no longer work with them, who would keep the central heating going? OK my son also works with PLCs, but it would rule out a call to the local heating engineer.

OK I am 75, so I do worry about my young wife of only 70 when I'm gone. But fitting a standard system means any heating engineer can repair it, if you're not there.

 

[elsmandino]

Thanks very much for all your input.

Just to confirm what I am up to:

I have a Y-Plan central heating and hot water system.

My current controller is on its way out and, as I am into home-automation, I am swapping it with one of these:

https://www.shelly.com/products/shelly-2pm-gen4

The only issue with this is that none of these devices come with SPDT switches, so (due to the way that Y-Plan is connected) I need to use a separate SDPT relay to control the hot water part.

Also, I need the SPST switch to update my Y-Plan system so that the actuator is not hold in the heating position when the boiler is not on - I know that the actuators are supposed to tolerate being held for days like this but it is a simple fix that should make it last a bit longer (I attach a diagram diagram that someone kindly added on another thread).