new boiler, radiators are not hot

[Tanya La]

Hello. We have got an open vent sistem. New boiler has been installed couple of weeks ago. Most of radiators get hot only on 5. We were told that pump is not powerful and needs changing. Is that so? Or there could be different reasons why radiators work only on full. We'll be really greatfull for your advice.

 

[nysk2008]

Muck in the system, was the system flushed?
What pump speed is it currently set on?
hat boiler and how big is the system?
Have you called in the installer to investigate?
Are the rad valves open?

 

[lame plumber]

or your rooms are hot enough already if its the trv operating only at setting 5

 

[TBServices]

My guess is there's nothing wrong with your boiler. You don't judge how warm YOU are, by burning your hands on the radiators. You just know you're warm enough.

 

[Tanya La]

Hello again. Boiler is vaillant ecotec 428. We have got 6 single radiators and 2 double. Pump is on 3. How well sistem was flushed we do not know. Valves are open. And another question, auto bypass was not put on. Is it important? What function does it have?

 

[doitmyself]

Boiler is vaillant ecotec 428. We have got 6 single radiators and 2 double.

Six single rads and 2 doubles is about 13kW; your boiler is 28kW, so it's massively oversized. Who decided what size boiler you need?

Use Whole House Boiler Size Calculator to find out what size boiler you should have.

I know it's too late to change it, but the output of your boiler can be reduced so it matches your requirement.

auto bypass was not put on. Is it important? What function does it have?

The bypass provides a connection between flow and return, after the pump, for when the boiler has turned off and the pump is in overrun to cool the heat exchanger down.
How many motorized valves do you have? If only one mid-position valve (three pipes connected) a bypass is not really needed as one port (rad/cylinder) is always open. But if you have two 2-port valves a bypass should be fitted as both ports could be closed when the pump is in overrun.