Vaillant & shower

[FERRARI81]

I have an EcoTec Plus VMW 35KW

During summer showers, the modulation required is around 13-15%

The problem is that when turned on the boiler tends to "open" at max or almost for 1-2 seconds and then starts to modulate. But that max is enough to send the DHW temperature above 63°C (48°C required) and then it starts to go on-off.

If, when turning it on, I open another tap for a few seconds, so as to allow for greater DHW consumption, the boiler manages not to turn off and can easily modulate the shower request.

Alternative solutions to opening the tap?

 

[Johntheo5]

I have an EcoTec Plus VMW 35KW

During summer showers, the modulation required is around 13-15%

The problem is that when turned on the boiler tends to "open" at max or almost for 1-2 seconds and then starts to modulate. But that max is enough to send the DHW temperature above 63°C (48°C required) and then it starts to go on-off.

If, when turning it on, I open another tap for a few seconds, so as to allow for greater DHW consumption, the boiler manages not to turn off and can easily modulate the shower request.

Alternative solutions to opening the tap?

Havn't heard of that model Vaillant but the eco tec plus 835 (35kw) has a minimum output of 7.5/8.8kw, you require ~ a minimum of ~ 5.25kw so the boiler will cycle on/off, at a present mains temp of 18C then you need a minimum boiler flowrate of 2.5LPM at 48C which is probaly also close to its minimum flow switch setting.

 

[FERRARI81]

But my problem Is only at the start, because before it modulates, it's open valve gas at max for 1-2 secs.

 

[Johntheo5]

One or two seconds would have little or no effect on the HW temperature, most gas boilers fire at ~ 65% and then ramp down fairly rapidly, vaillants were notorious for maintaining this firing rate for 60 secs or so, at least in CH mode, not sure about DHW mode. How long is it taking the temperature to rise from the start of firing to reaching 48C and then 63C?

What do you reckon the flowrate is after you switch off the "start up" tap?