Heatmiser and Salus wiring centres & Vaillant system boiler - call for CH

4 Oct 2021
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United Kingdom

I wondered if anyone would be kind enough to give me thoughts on how best to make a call for central heating (the hot water side of things is fine) to a Vaillant (630) system boiler, possibly via a switched live connection.

The system involves UFH without radiators – UFH on the ground floor and also the first floor. Two Heatmiser UH8-N wiring centres are used, these are located next to the two UFH manifolds. The local thermostats, pump & valve are wired in to their respective Heatmiser wiring centres. Volt free Heat Enable connections -live, switched live and also earth - are then fed back from the two Heatmisers to the Salus TC100 wiring centre which is next to the boiler.

At this point, according to the Salus TC100 wiring diagram (uploaded), the Thermostats (or in this case the Heat Enable connection) would then be connected to the local central heating motorised valve which, sensing the call for heat, would operate and in-turn fire up the boiler via the connected live boiler wire which runs to the Vaillant boiler.

Because there is no central heating motorised valve local to the boiler (they are both local to the manifolds and so wired into and operated by the Heatmiser wiring centres), I believe that I may need to connect the volt-free Heat Enable switched live / live feeds which are coming into the Salus TC100 to the 230v switched live connection which runs to the boiler (rather than the live?), so that the call for the central heating can successfully be made.

Any thoughts on a good solution would be greatly appreciated!


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Not sure exactly what your asking but if you put 230vac on the LS connection in the uh 8 you will have 230vac on the LR which is the boiler enable , this would connect to the boiler switched live, you dont say how the hot water is controlled.
Hi Picasso. Thanks so much for taking the time to reply.

At the moment the boiler is running all the time (continuously displaying either the solid radiator symbol or flashing radiator logo), heating up to the set target flow temp on the boiler. Once this temp has been reached the egg timer symbol comes on and the boiler relaxes until the target flow temp drops by a few degrees and then the cycle repeats.

Your suggestion to add a 230v live feed to LS on the Heatmisers is greatly appreciated. I'm hoping that then connecting Heat Enable LR and the boiler switched live will then provide the necessary instructions to break the cycle!

The hot water is controlled via a thermostat local to the boiler and cylinder - these are hooked up to a local cylinder hot water valve and a secondary hot water return pump.

I'll try your suggestion later this evening and will report back.

How old is the system and has this problem always happened?
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Thanks for your replies chaps.

The system is new. My plumber friend and I have fitted the system and this issue has been present since we first turned it on. An electrician is scheduled to visit next week to provide official approval on the electrical side of things, it would be nice to figure out this perplexing aspect beforehand though!

The 24v link hasn't been removed Picasso - it's still present in the boiler. Should this be taken out to work with my setup?

Guys you were spot on! The 24v link has been removed and there is silence at last!!

Thank you so much for your help with this, i'd have continued blaming the poor wiring centres for this issue had you not pointed me in the right direction.

Adding a permanent live to the Heatmiser Heat Enable LS connections has allowed successful communications to take place between the LR and boiler switched live connections too. Thanks a million Picasso :)

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