Flow and return temperature differences



I have a worcester bosch greenstar 40cdi condensing regular boiler. I have 22 rads and a 250litre cylinder also my house is very long so the pipe runs are very long. The heating is on two zones (upstairs and down stairs) My problem is that the instructions state that the temp difference between the flow and return should be 20*. The flow is 81 when it leaves the boiler but when i returns it is down to near 50*. Is there anything I can do ie bigger pump? or is it ok how it is? Also it is quite hard to balance the rads so they all get hot as each other would a bigger pump fix this too? thanks
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make sure your bypass rad is big enough ie when all the other trvs shut down. you could fit a auto bypass on system.
You again?
I thought you said you wanted a boiler but

I have 22 rads two bathrooms and two heating zones (upstairs and downstairs) and a 250litre unvented cylinder. I want a worcester bosch boiler but what size would be best?


I have a worcester bosch greenstar 40cdi condensing regular boiler.

ha ha i wasnt getting anyanswers so I thought i would try from a different angle! There is an auto bypass fitted should i open that up more?
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Is there anything I can do ie bigger pump?

What do you have :?:

A 15/50 will probably be too small. Depends on the bore of your pipes amongst a lot of other technical stuff i can't be bothered explaining.

There is an auto bypass fitted should i open that up more?

What for? To cool your radiators even more?
its 22mm pipe with 10mm tails to the rads would a bigger pump help or not? I have tried balancing the system and most get very hot and a couple get warm the upstairs zone works perfectly its just the downstairs
Has the system ever worked properly?

What times of the day do you have the boiler running?

What room stat temperature setting have you selected?

I'm not interested in how many rads you have downstairs or upstairs.

What size pump do you have and what is the diameter of the main runs from the boiler through the pump to where it branches up and downstairs and what are the size of branch pipes
it works fine when the hot water is hot enough. my main conserne was with the return temp being so low. will it damage the boiler? as the instructions says that the temp diff should be 20* and it is 30+* the water still leaves the boiler at 81* like it should
the boiler is next to the cylinder it runs 22mm copper from the boiler into the pump then 0.5m to the zone valves where it branches off (dont know the pump size)
All the rads get hot when the H/W zone valve closes. but the low return temp remains
Your pipes are too small. 28mm minimum from boiler through pump, 22mm branch for HW 28mm out to branch to downstairs/upstairs possibly 22 ok from there.

Pump make and size is written on the front of it.

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