Flow & Return Temp issues

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Hi all.

Newly signed up to this forum, but have searched extensively for information on this one.

Logic Max combi 30
8 radiators, all nice & balanced with around 10-12 degrees drop
3 rads are vertical ‘designer’ style.
All rads have TRVs, don’t have a ‘bypass’

Problem:
(1) I can’t get the boiler to condense due to the return and flow temp (read from directly at the boiler menu screen) being more or less equal. Flow 75 return 65 (10 delta). At times the difference is sometimes less than 5 degrees.
(2) the designer rad in the bedroom clicks and bangs when heating first starts. TRVs and L/S are installed in a mixed fashion, but all are bi-directional.

problem solving so far:
Perfectly balanced all rads. All rads run hot no air.
Removed small amount of air from b/room towel rad
Adjusted boiler flow temp up & down
Adjusted pump speed up & down - choice of 70% or 100% only it seems ?
All TRVs removed, pins move freely, and replaced.
Tied down all pipes, no sides in pipes rubbing furniture or joists.

Side note. my thoughts so far from research: radiators not well sized enough. Air lock causing the banging. Not having a ‘bypass radiator’. Banging noise could be from a faulty TRV? TRV and Lockshield the wrong way around on some rads (unlikely). Pump speed is too high, it’s returning too hot to the boiler.

my main priority is to stop the banging noise in the bedroom and it’s driving me mad.

my heating engineer balanced the system according to his ‘all lock shields kept fully open and use the TRV to control temp’. I wonder if I should return to this method. I’m hesitant to as I’ve just got all rads well balanced.

any ideas?
 
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Reduce the flow temp first and look if you can get WC controls to dynamically change flow temps, also check if boiler has been scaled correctly with max kw output
 
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Thanks pal.
Reducing the flow temperature to me sounds counter-intuitive. The higher the flow temp, the less the difference with the return temp? I will try this right now.

sorry a bit of a DIY question. What’s a WC control?
 
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Thanks pal.
Reducing the flow temperature to me sounds counter-intuitive. The higher the flow temp, the less the difference with the return temp? I will try this right now.

sorry a bit of a DIY question. What’s a WC control?

WC weather compensation

If you have you boiler sized too high and its not scaled back then it will heat up the water too quick for the heat lost by radiators. Ie you have a 10kw heating requirement but boiler puts out 18kw etc, it will heat up too much.
Without smart controls like WC, room comp etc, most boilers will fire at full until near temp then scale back, but may overheat too quickly then cycle etc.
It's not simple one fix.
 
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Also you loose less heat in pipes if flow temps are lower, useful if you pipes are, under floors or enclosed etc.
 
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Quick update: decreasing the flow temp

result - the return temp is now more of less equal to flow

flow 65
Return 62

this can’t be efficient, but all rads are warm. So should I just stop being fussy and leave it until the next boiler service and engineer visit?
 
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Given your most recent comment - as long as the rads stay warm, plenty of inhibitor, and it doesn’t cycle on/off I am just going to leave it.

our heating engineer will come back after summer to carry out service. Then is probably a good time to bring this up and get it done properly?

Is there a setting I can access to adjust the power outputs, or is the boiler ‘smart’ and does this itself?

many thanks for taking the time to inform me
 
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Given your most recent comment - as long as the rads stay warm, plenty of inhibitor, and it doesn’t cycle on/off I am just going to leave it.

our heating engineer will come back after summer to carry out service. Then is probably a good time to bring this up and get it done properly?

Is there a setting I can access to adjust the power outputs, or is the boiler ‘smart’ and does this itself?

many thanks for taking the time to inform me

Might be little you can do if your boiler can not modulate any lower vs the heat loss, ie if you need 3kw to maintain temp but boiler can not go below 6kw then the water temp will continue to rise until it cuts out.
 
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Thanks well at the very least you’ve helped make sense of the situation for me

many thanks
 

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