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https://www.diynot.com/diy/threads/wiring-a-viessmann.248503/post-1794427 See post 4 on this link.

As per attached trouble shooting steps; the fan starts as soon as boiler is switched on but then it doesn't get to ignition stage and I don't see any error message on display, it just shows water temperature on screen.

Its a wired Drayton Room stat (old dial type). This is how I get into Serv mode.

Yes, Pump is connected to the wiring center, when there is call for heat, I can hear the pump circulating water when boiler fan starts its purge cycle.

I have tried bypassing the Room Stat and tried to connect boiler directly with same result. It doesn't fire up. It only fires up when I reset it and it goes in 'serv' mode. The boiler and pump are connected to the wiring center. Wiring center N,L and E is fed by Spur. The Programmer and Room...

Yes. When the thermostat calls for heat; fan on boiler starts and after a brief period shutdown. The screen shows the water temperature starts from 100deg C and quickly goes down to 30s. It stays there forever. I then have to reset the boiler by turning the CH knob to reset and then counter...

I don't mind that at all. Thanks for clarifying, after all I was led by your guidance to get this far! It is Drayton wired Room Stat. Correct. Surprisingly, the balancing was very smooth and I got nice even temperature at all rads @ C2 setting. With external pump, should it be running all the...

C2 was indeed the setting that balanced all rads. I had already marked the flow on rads so balancing was smooth and all rads heated up nicely; the farthest one on the circuit took its time but it got to the temperature at the end. Correct. Why would you say that now that I have followed BS for...

Have you considered using oil or LPG for space heating? Don't know about LPG rates in UK but it would be cheaper than electricity for sure.

Thanks, probably I have only balanced the first two rads which are closer to the boiler and not others. I need to balance the rads first and then set the pump speed? I thought setting the pump speed first and then balance the rest of the radiators.

What about other PP settings? I haven't tested it yet.

I don't understand its settings clearly and I have tested it on c3 (max speed) but thought I ask before switching it to other settings. Based on my load which setting should I run it on. My back of the envelope working indicates a flow of 600 litres/hour based on a load of 9kw? Based on this...

Flomasta make with 6m head. No ABV installed. CH Current load - 10-12kw with 10 rads. As per my Heat loss calculations, I have oversized radiators by ~30-35%. Essential load (2 double panel rads, 48 and 40 inches; 2 single panel rads 55 inches each; 1 fan coil unit ~2.5kw + 3 small bathroom...

Update : I thought I'll update people who helped me with the install process. To summarise 7 pages; the location where I wanted to install the boiler had a height constraint of 7 ft as I wanted to install Viessmann heat only boiler as OV. The min head required was 0.1m from water level in...

Yes Sir, Thanks.

CBW - Thermostat is an old school analogue one but I have put a 3 core cable from lounge to the boiler; in case I want to upgrade to a fancy Thermostat/Controls in future. Flameport - Yes and Thanks for explaining it in simple terms to me. Much appreciated.

I know, you are right but I have separate HW arrangement via direct source so not using it with CH. I want to use simple programmer and thermostat to switch heating on via programmer and thermostat. I have made connections in the attached wiring circuit for boiler and pump, how do I wire...

Hi, I have a heat only boiler for central heating only, not installed or commissioned yet. I am trying to understand electrics; e.g I got a wiring center (pre wired) for Y plan system. At this stage I only want to control Central heating through programmer and thermostat (no hot water). The...

Please share the gas consumption difference wrt your old boiler, if you can?

I am not in UK but I have told you the dimensions of rad and room and it made a difference in my case since you asked. I am sure a lot of folks in UK would have similar experiences.