Selecting combi heat outlet and balancing system

[mole]

I have just replaced my clapped out Ocean combi with a Ravenheat condensing combi which uis working fine. Now I would like to balance the system correctly.
I have a pair of pipe thermostats for adjusting the 11 Degree differential between flow and return but need help on how to determine the setting of the bypass valve - Ravenheat states that it needs to bypass a flow which exceeds the minimum 503 lt/hr when burner is firing. How do I determine this rate without using some sort of flow meter.
Would it be practicable to close down all radiator flow valves (thermostatic!) with the bypass fully open and then slowly close it until the system became noisey or the overheat thermostat cut off the boiler?
Final question - the boiler comes with the output set at mid range, about 60000Btu/h and my system requirements are about half that. Is it essential that I have the output adjusted to the minimum which is just about what my systen requires. If I leave it as it is, what effect will it have on the system efficiency and will it give rise to rapid recycling and perhaps a noisey system?

 

[ChrisR]

I've never fitted a Ravenheat - most pro's won't touch them. 11º? Not the norm for a condensing boiler. Balancing isn't so important with TRV's as they sort themselves out to a fair extent. Start by opening the rads near rthe boilerust half a turn and see how it goes. Your pump is more than capable, so as long as the furthest rad heats up quickly you won't benefit a lot further by meticulous balancing, which is an iterative process taking a long time.

Do you have one radiator without a TRV?, and a room thermostat?
Setting bypass: You wont know what the flow through rad just mentioned is, but the flow through the byypass can be seen from the pump flow graph, which should be in the mfrs lit. You'll see what the flow is for a given head - set the head a tad higher to allow for the un-TRV'd rad.

 

[mole]

I have neither a rad without a trv or a room stat. Could you please simplify your reccomendations regarding the bypass valve setting - you have lost me technically - how to I convert a head figure into the number of turns of the scredriver adjustment on the inline bypass ballvalve?

I have just replaced my clapped out Ocean combi with a Ravenheat condensing combi which uis working fine. Now I would like to balance the system correctly.
I have a pair of pipe thermostats for adjusting the 11 Degree differential between flow and return but need help on how to determine the setting of the bypass valve - Ravenheat states that it needs to bypass a flow which exceeds the minimum 503 lt/hr when burner is firing. How do I determine this rate without using some sort of flow meter.
Would it be practicable to close down all radiator flow valves (thermostatic!) with the bypass fully open and then slowly close it until the system became noisey or the overheat thermostat cut off the boiler?
Final question - the boiler comes with the output set at mid range, about 60000Btu/h and my system requirements are about half that. Is it essential that I have the output adjusted to the minimum which is just about what my systen requires. If I leave it as it is, what effect will it have on the system efficiency and will it give rise to rapid recycling and perhaps a noisey system?

 

[oilman]

If I leave it as it is, what effect will it have on the system efficiency and will it give rise to rapid recycling.......

Common problem with oil and gas boilers, loads of heat, and yes the boiler starts and stops, gets too hot, scales the heat exchanger, just to provide enough heat for 2 to 3 days per year. Altering the temperature of the boiler with the thermostat is not really the cure, so turning down the heat is a good move IMHO. Efficiency is difficult to establish, but the nearer the heat output is to the load, the better.

 

[ChrisR]

OIlman is spot on as usual but I can't suggest you alter the boiler's output as you can't check it - corgi territory.

To comply with building regs and, frankly, common sense, you should have a root stat. The rad nearest it should have noTRV.

If you had an "Automatic Bypass Valve", which is a thing designed for the purpose, you would be able to set it as I described. It only opens if enough of the TRV's are shut to raise the pressure across the system. If you just have a small service-type valve then a) expect it to leak and b) it only takes 1/4 turn to open it fully and you are guessing.

"Would it be practicable to close down all radiator flow valves (thermostatic!) with the bypass fully open and then slowly close it until the system became noisey or the overheat thermostat cut off the boiler? "
You don't want the hi limit stat to be any where near operating, and unless it locks the boiler off you wouldn't know which stat it was anyway. Go the other way - leave the bypass open and see if all the rads get hot - my guess it that they will.