Hi Guys, I wonder if you could help me understand my central heating system a little better. Here's the setup.
New Vaillant Ecotec Plus 832 combi boiler connected to older system of 7 flat panel radiators in 3 bed semi.
Boiler fires up and burner and pump are at low settings for a few minutes. Burner and pump then increase and heat the water in the system to the target flow temperature. After reaching target flow temperature the boiler and pump modulate to the boiler's lowest output (5.2 Kw) and slowest pump speed (15%). The drop across flow and return is 12 to 15 degrees C to start with. It falls to 4 or 5 degrees C when system water is up to target flow temperature. This is the same irrespective of the LSV settings (even when fully open). All radiators get hot and have been bled of air.
Before the target temperature on the room thermostat is reached the system water temperature rises to 4 or 5 degrees above its target temperature (sometimes before upstairs TRVs shut down and definitely after they do). In other words, the return water is then at the target flow temperature. The boiler then goes into anti-cycling mode.
When the anticycling time has lapsed the boiler fires up, gradually raises the system temperature to 5 degrees above target and anti-cycles again. It continually repeats this process. Consequently, the target room temperature is never reached or is reached very slowly. The system water temperature and anti-cycle period are controlling the heating not the room thermostat. It's as if the boiler cannot modulate low enough to maintain the system flow temperature and/or the radiators cannot emit enough heat to stop the system return water temperature rising above flow target (i.e. to balance heat input and heat loss).
Is this normal? I would have thought the goal is for the boiler to modulate to maintain the target flow temperature until the target room temperature is reached. Then the room stat will switch it off and along with the anti-cycling period, keep the room at target temperature within half a degree or so.
New Vaillant Ecotec Plus 832 combi boiler connected to older system of 7 flat panel radiators in 3 bed semi.
Boiler fires up and burner and pump are at low settings for a few minutes. Burner and pump then increase and heat the water in the system to the target flow temperature. After reaching target flow temperature the boiler and pump modulate to the boiler's lowest output (5.2 Kw) and slowest pump speed (15%). The drop across flow and return is 12 to 15 degrees C to start with. It falls to 4 or 5 degrees C when system water is up to target flow temperature. This is the same irrespective of the LSV settings (even when fully open). All radiators get hot and have been bled of air.
Before the target temperature on the room thermostat is reached the system water temperature rises to 4 or 5 degrees above its target temperature (sometimes before upstairs TRVs shut down and definitely after they do). In other words, the return water is then at the target flow temperature. The boiler then goes into anti-cycling mode.
When the anticycling time has lapsed the boiler fires up, gradually raises the system temperature to 5 degrees above target and anti-cycles again. It continually repeats this process. Consequently, the target room temperature is never reached or is reached very slowly. The system water temperature and anti-cycle period are controlling the heating not the room thermostat. It's as if the boiler cannot modulate low enough to maintain the system flow temperature and/or the radiators cannot emit enough heat to stop the system return water temperature rising above flow target (i.e. to balance heat input and heat loss).
Is this normal? I would have thought the goal is for the boiler to modulate to maintain the target flow temperature until the target room temperature is reached. Then the room stat will switch it off and along with the anti-cycling period, keep the room at target temperature within half a degree or so.