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Hi, I have a Fan Coil unit in lounge and radiators in Bedrooms and Bathrooms. I also have a wired thermostat in Lounge with the boiler which is set to 19degC. Issue - FCU never turns off, it keeps running, if boiler is firing, FCU will blow hot air but when Boiler trips and as water temperature...

See attached

I measured the distance from floor to the base of the radiator; in my case it was ~8 inches. I had some wooden pieces lying in house; I stacked them to get to the desired height - 8 inches. Put radiator alongwith brackets on those wooden pieces to align the pipes. Then mark edges of the brackets...

Theoretically speaking and what I have read in books, I think you need to know: - the head loss of your system (depends on pipe size, flow rates, design and layout of rads) so you can draw system curve of your heating system. - pump curves of your model from manufacturer which will tell you...

but that would defeat the purpose of heating, wouldn't it? What would happen if we oversize the rad but keep the flow rate at 50?

can't attach links from youtube. search for heatgeek Y plan wiring; there is a series of 4 vidoes on youtube; 3 are for S plan but part 3 is for Y plan. Watch it.

John also helped me as I also have similar pump (newly installed). see attached for application of CC or PP and other modes, basically its what stated above but in a tabular format for future reference.

I was looking at another forum and came across this excerpt from MI for a combi boiler. I followed the instructions and it worked.

Just to be sure check out which one is yours; heat only or with DHW https://viessmanndirect.co.uk/AdditionalDepartments/Header-Content/Weather-Compensation

Most probably. The tech support should have picked it up and I specifically asked about resetting all controls, even then they came up with Plate HEX and gas control valve!

For anyone with flame intensity stuck at the lowest level on vitodens; see attached. Even though the instructions apply to combi variant, I can confirm that it also worked on heat only version of the vitodens as well and after following the instructions the CH dial now behaves as it should...

Success! finally. For anyone with flame intensity stuck at the lowest level on vitodens; see attached. Even though the instructions apply to combi variant, I can confirm that it also worked on heat only version of the vitodens as well and after following the instructions the CH dial now behaves...

yes, heat only boiler 13kw for CH only, I know its tight but my essential load running most of the season is 6kw. It gets below 5 for a week and for that I have auxiliary heating arrangements; mini splits in all rooms.

Thanks John, perfect. It feels good to know that I have sized it correctly.

Thanks, theoretically boilers are sized based on HL and design temp, since rads are almost, always oversized. I didn't know about HL of my propety and previous 24kw boiler worked with 8min on and 12mins off cycle (in slightly less cold weather the off time was doubled than on time), I was told...

Thanks John, Yes that's correct 11.34 is what I require based on my designed temperature is 5deg C outside temperature so my dT would be 15degC (assuming room temp of 20degC). or What flow temperature should I be running on in my scenario?

So theoretically you are saying at 5degC the boiler flow shold be 59.4 as per the Excel table of OT above to heat the house effectively, correct? I did something similar but I agree with John that boiler flow needs to be adjusted as per outside Temperature. I keep mixing OT open therm with...

I am not a pro but DiYer like you; how rads closer to the boiler are performing? Do they get hotter than rads further away from boiler.

Couldn't agree more. The pipe length is not unusual, its hardly 15 ft from gas service line which is 1.25" from meter. I also asked viessmann about min pipe diameter for gas line, their response: 'MI asks fr 17mbp at the valve before fire'. I also stand corrected on WC for gas which is 20mbar...