Danfoss heatplan - unsafe wiring guide

[FurstyFerret]

I've just moved home (it's new build but I'm second owner) and come into possession of an unvented hot water system. There's a wiring guide included with the book of manuals and a quick look inside the wiring centre suggests it's been adhered to.

However, it appears to be an unsafe implementation and can, in effect, completely bypass both cylinder thermostats under the right scenario.

They've set it up so the switched live from the programmer goes to the cylinder thermostat, then to the motor L on the valve. The permanent live on the valve (ie, grey) is just that, permanent.

What happens if the valve jams in the open position - or is manually operated by the homeowner? The hot water will run continually until the boiler cuts out or the cylinder over-temp protection vents the water?

Danfoss are still publishing the same wiring guide.

Similar here:
http://www.electriciansblog.co.uk/wp-content/uploads/2012/02/S-Plan-Twin-Zone-Wiring-Diagram.png

Worth getting a plumber in to correct this?

 

[D_Hailsham]

They've set it up so the switched live from the programmer goes to the cylinder thermostat, then to the motor L on the valve. The permanent live on the valve (ie, grey) is just that, permanent.

Is 'motor L on the valve' the brown wire?

If so, the wiring is the standard way of wiring two motorized valves -aka S Plan.

What happens if the valve jams in the open position - or is manually operated by the homeowner? The hot water will run continually until the boiler cuts out or the cylinder over-temp protection vents the water?

Yes the boiler will run if the valve sticks open or the microswitch contacts weld together. There are literally hundreds of topic on this forum about exactly this problem.

Manually opening the valve normally does not cause the microswitch to close. The manual position is provided to give a clear path when refilling the system.

 

[FurstyFerret]

Is 'motor L on the valve' the brown wire?

Yep, that's it. Didn't want to give colours because I'm not sure if they're standard across all motorised valves.

Thanks for the reassurance. I couldn't find other threads in a quick search but imagine I was looking for the wrong thing.

Can a normal system boiler actually over-pressurise /overheat (same thing I suppose) a cylinder if this happens, or do you just get very hot water? My boiler controls only allow a maximum of 80C anyway.

 

[Whitespirit66]

What happens if the valve jams in the open position - or is manually operated by the homeowner? The hot water will run continually until the boiler cuts out or the cylinder over-temp protection vents the water?

Life is full of what ifs. Millions of homes in The UK will have motorised valves wired like this. There are other failsafes built into modern boilers and unvented hw cylinders in case of over temp/pressure. I wouldn't lose sleep over it.

(it's new build but I'm second owner)

I've got a new Cortina for sale. Only 2 previous owners.