Old thermostat not working

[martin_2442]

Hi Folks, looking for some advice.

I have an older style Sabre boiler and an old 'Acl' thermostat in the hall.
(see pics) The thermostat has never worked since I moved in a year ago and does not power up.

I removed it and have attached photos of the wiring. Looking to see what thermostat is best to replace it with, looking for something cheap that will do the job...preferably a digital one but don't know what would be compatible.

Thanks in advance!

 

[ericmark]

I know nothing about Sabre boilers, so there are three ways to control the boiler output in general.
1) The return water temperature.
2) Digital control i.e. on/off.
3) Analogue control i.e. up/down.
Analogue is the best, but not all boilers can use analogue wall thermostats, but using the return water temperature is also analogue control, so the TRV's can control the boiler output.

However there is a problem using TRV's, they can't turn whole boiler off when not required, it will cycle on/off at lowest output all summer with just TRV control, so we want some automated system to turn the whole boiler off when all rooms are satisfied.

So we still need that wall thermostat, set at the upper end of the range of the TRV in same room, so on a warm day it will switch off.

However I don't want house same temperature throughout the day, so I want a programmable thermostat both the wall and TRV head, but now the nitty gritty how much do you want to pay, some thing like the Honeywell EvoHome or Drayton Wiser will clearly give you full control. But a wired on/off programmable thermostat powered by a pair of batteries will cost around £35. And no question they will work, but to set the lock shield valves and TRV head with the wall thermostat is not easy.

My TRV head shows current and target temperature current it says is 20.3ºC hard to read on picture, but I can use the two readings to set the lock shield valve, I used a thermostat like this for years, it cost around £35, powered by battery simple on/off. But tried cheap wireless and it lost the RF link, and was a real pain, so once you go to wireless, the cost jumps to around £125 to get one which will fail safe.

We are seeing some really cheap thermostats on the web as to how good I don't know. £26 is darn cheap, as to how good they are not a clue, is it worth taking a chance?

 

[Taylortwocities]

Hi @martin_2442 As you can see, our friend @ericmark loves to throw in a few thousand words and a couple of curved balls. I bet you are more confused than you started with? He loves to throw in spurious stuff about controlling TRV valves (that you don't have), modulation, OpenTherm and other stuff.

Your old thermostat, like most is a simple switch. There should be a diagram inside the ACLfront cover. Can we see that?
Obviously a simple thermostat will probably do.

Questions:
Do you already have something that controls on/off times?
If you went "digital" what do you want it to do? Obviously these can control times, some can be controlled over wifi, integrate with smart speakers, allow you to turn the heating on from your sunbed in Turkey......

 

[martin_2442]

Thank you all for your replies. I have attached a photo of the inside of the case. The only reason I am thinking digital is to have an accurate temperature reading. Not looking to spend a fortune on a hive system at the moment...simply something that's works for now!

 

[RandomGrinch]

There are only 2 wires (plus earth) to your 'stat, you don't have a neutral.

If you want to keep things simple, cheap and don't want to change the wiring, you could replace it with a simple dial stat...

Drayton RTS8 1-Channel Wired Room Thermostat - Screwfix

Order online at Screwfix.com. 2 or 3-wire installation. FREE next day delivery available, free collection in 1 minute.

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Alternatively, you could have a battery operated digital stat. Something like...

Error 410 | Screwfix

Thousands of products at low trade prices | FREE next day delivery available | 30 day money back guarantee on all orders.

www.screwfix.com

Or for a 'smart' experience, you could try a Nest Thermostat E.

Google Nest Thermostat E

Comes with energy saving features and a simple schedule that's easy to adjust. Can be controlled from anywhere with the Nest app.• Turns itself down after you’ve left, so you don’t heat an empty home• Shows the temperature when you're close to it, then disappears when you walk away• Use your...

www.toolstation.com

Other choices are available!