Condensing boiler - balancing system?

GreySquirrel

We have a new condensing boiler retro-fitted to our existing system: 8 rads some with TRVs.

Setting the flow temp at 75 degrees C and with the pump at its lowest setting, the boiler return is about 60 degrees C.

Manual says aim for a 20 degree C drop across flow and return. How should I go about balancing the system?

I haven't quite grasped the theory behind condensing boilers. Is it the return temp that is important to achieve high effiency? If so, what is the figure?

stillbornalive

have you had an automatic bypass valve fitted to the system.

http://content.honeywell.com/uk/homes/Catalogue/Non%20Electric/5.1%20DU145.pdf

GreySquirrel

Nope. And manual says it doesn't need a bypass.

Have a look http://www.condensingboiler.org.uk/ .

GreySquirrel

gary71,

Had a look. Good info. Also

http://www.rvr.ie/default.aspx?subj=html/condensingboiler.ascx

Good graph.

copper12

A return temperature of 60 degrees on a domestic system with radiators is about as good as you can get

In respect of balancing your system, as you have trv's fitted they will when they reach the set temperature stop the flow of water into the rad changing the characteristics of the flow of water in your heating system, which will impact on your return temperature ie..if you have 4 rads with trv's when they are up to temperature you will go from a 8 rad system to a 4 rad system, Gary

GreySquirrel

balancing with TRVs fully open

Micky Dolenz

Turn down flow temp. you really want 55 degree C return temperture to take full advantage of your boiler.

GreySquirrel

Balancing rads. Getting a 12 to 15 degree C drop. All are hot. Will lower boiler temp and try to get a lower return temp to boiler

Micky Dolenz

Have you adjusted balancing valve on return to cylinder?

to really acheive it in a standard installation you may need to increase size of radiators.

GreySquirrel

Cylinder return valve closed while I balance rads. Three upstairs rads are very old single panel no fins. We hope to change them next year.

With the LSVs open I get about 10 deg C drop on upstairs rads and about 15 degree C drop on downstairs rads. 10 deg C drop on a kickspace rad. Drop across boiler about 15 degrees C

Micky Dolenz

I would balance with return valve to cylinder open, as it would be through normal operation of system. It will effect your flow and return temps. adjusting this valve right is key.

GreySquirrel

Do I treat it as a lock shield valve? It's a 1 inch flow and return to the cylinder.

Micky Dolenz

exactly.