Discuss Viessmann boiler question in the Central Heating Forum area at PlumbersForums.net
... really needs more water. Ideally, you'll have a buffer tank added to the system.
If the boiler is connected directly to the radiators occupants may notice the pulsing on/off. Some people seem more sensitive to this than others. The problem can be mitigated by means of a 'buffer tank', which smoothes out the temperature fluctuations arising from the on/off action of the boiler.
The installation manual says that the minimum output is 4.3kW @ 80/60C or 4.7kW @ 50/30C. If the house really needs 26kW for heating then the boiler will only go into on/off mode when the outside temperature is about 17C.IIRC, your boiler's minimum output is 9kW (1:3 turndown) so when the demand from the emitters is low, which it often will be in a well-insulated and zoned house, the boiler will be providing short pulses of 9kW in an attempt to meet the demand.
Weather comp sensor automatically adjusts the rating and temp so you will get it running constantly
That isn't much help on a 16C day when all you have is 3:1 and you need 20:1.
I agree re your Firebird boiler, I have one for the past15 years and it has never locked on any fault condition, however, we are where we are.
To rule out constant cycling when the rad(s) output is > the boiler min output you might consider the following or at least run with both CH zones and all l/shield+TRVs opened if the boiler/system is already up to temperature, also roomstats turned up fully:
You have 12 rads, don't know their combined output but assume ~ 18kw and total system water contents of say 80 litres., can you switch in the two heating zones (from cold conditions) with all rad lock shield valves & any TRVs fully open, assuming a boiler SP of 70C then the boiler should fire (100%) continuously for ~ 25 to 30 minutes to reach SP temp and should then continue to run continuously in modulating mode at ~ 58% say 15 kw output. If any big deviations from this then you have a problem but you have to start somewhere. Also as mentioned above, check the setting of the ABV just below the boiler, I would suggest shutting it off (index 0.6 0r 6?) initially and if no problems then set it to ~4.
install a 200 will modulate down to 17:1 or if you can get an older one 20:1
I agree it is possible to fight this problem with technology. Maybe they will develop the "infinitely modulating boiler" that is permanently on at whatever percentage is required for the demand. However, one has to question the expense/complexity/robustness of that solution, when a simple tank of water can solve the problem.
Reply to Viessmann boiler question in the Central Heating Forum area at PlumbersForums.net
We get it, advertisements are annoying!
Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.