Alpha CD20S boiler wiring issue

[jerseysimon]

Hi,

I was looking to install a Nest thermostat and started trying to understand the existing wiring to work out how to add. The boiler is an Alpha CD20S and is currently set up (in my limited understanding) in a S plan configuration (2 valves rather than 1) as part of a pressurised hot water system with a megaflow style cylinder (different brand). The existing thermostat is a salus RT500RF, which is wired into the system using a Salus TC100 wiring centre.

My question is this... according to the boiler manual if a thermostat is used the boiler should be fed with a continuous mains feed, and then the thermostat should operate a switched live feed to turn the boiler on.

However when I was tracing the wiring it was obvious that it had been installed such that the mains feed is being turned on and off itself. i.e. when the thermostat is off the boiler receives no power whatsoever. This has been like this since we had the boiler installed a couple of years ago but is this an issue? My limited googling suggested that e.g. the boiler might want to run a pump or similar after the gas has been turned off to draw off excess heat. How worried should I be or is just a different approach?

Link to boiler manual (page 5 for wiring):

http://www.alpha-innovation.co.uk/custom/upload/instructions/CDS/CD S Inst & Serv Inst 01-11 .pdf

Thanks very much in advance

Simon

 

[Groovejet]

So what about when the thermostat is off and you say boiler is off...Is the boiler coming on where there is a demand for Hot water (Cylinder heating up??)

And have you checked that the power is categorically OFF and doesnt stay on or come on for a short while as a pump overrun

 

[Dan Robinson]

It is a scarily common installation error and one I had to resolve for an unsuspecting lady last week.


How installers can make such basic errors is beyond me. . But there we are. . The benefits of a trade beaten down by customers who know the cost of everything and the value of nothing compounded by leftie vegetarians wasting our TV licence on shyte like Roguetraders and Anne Robinson's extensive craving for botox.

 

[jerseysimon]

Hi,

Thanks for the response. Haven't traced the full wiring but yes 99% sure that the boiler is fully off. The switched live terminals (1&2) are still connected together with the L/N feed being the only connections.

Another data point is that the light D doesn't remain continuously on, but rather only comes on when the thermostat or hot water cylinder are calling for heat. Page 25 of the manual implies that this light should always be one whilst the boiler has mains power.

Will confirm with a multi meter that the main feed is indeed being cut immediately but all the info I can see points towards this.

WHat are your thoughts?

Simon