SwitchMaster SM400 replacement

[West Counrty DIYer]

Hi

My switchmaster sm400 seems to be broken. The boiler works fine on constant but on the timed function it seems to turn on and off every 15 seconds or so and makes some odd noises.

I'm assuming that its time to replace the sm400. I'm hoping for a recommendation please, something I can go get asap from Screwfix or similar.

I've seen a couple of threads but they are quite old the suggested replacement is now not available.

I'm pretty sure I have a gravity system, CH is controlled by a motorised vavle, I can only have HW or CH&HW not CH on it's own.

I'd like to fit a thermostat as well, wired is fine and it's not essential.

 

[stem]

Someone asked the same question a couple of years ago. You can find the thread if you click here. Post back if you need any more specific help. You might like to consider a Hive Dual Channel. That would replace the SM400, it can be set to gravity and comes with a wireless thermostat included.

I'm a little intrigued by your system, usually the old gravity systems don't have a motorised valve on the heating. The hot water is heated by natural gravity circulation and the radiators heat up when the pump is started. A motorised valve on the CH is a bit unusual, but maybe the radiators were also getting warm because of gravity circulation and the valve was inserted to stop that happening.

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[West Counrty DIYer]

Hi, thank you. So my system seems to work thus, I can select hw only or hw & ch. I have a hw tank up stairs. There is a motorised valve that operates to allow the ch to work ( I had to replace it last year).

I'm interested in your hive dual channel suggestion is there anything I need to look out for, the drayton controllers on the screwfix app say if they are suitable for gravity fed systems, the hive ones don't mention it. Would this one be suitable?

Hive Active Heating Thermostat V3 Hot water Hubless | Toolstation

• Daily heating & hot water schedules • Automatic frost protection • Ready By pre-heating • Holiday mode • Touch screen control • Works with Amazon Alexa, Google Assistant & Apple Homekit For use with system and conventional boilers with a separate hot water tank. Designed for new...

www.toolstation.com

I have an Amazon Alexa so I believe I have a hub to run it.

 

[stem]

The Hive Dual Channel Receiver can be set to gravity circulation. Here's how it's done from the Hive manual. I've not worked on the Hubless version, but the receiver looks to be the same.

When it's in the gravity and part pumped mode, whenever the CH is set to be 'on' the HW will be on as well.