Yep understand ... control head fully open (or TRV) and adjust via lockshield ........... will have another go when I change the rad
Combo Boiler issues
- Thread starter RickH
- Start date
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What temperature differential are you trying to achieve and how are you measuring it?
It's having the correct flow which is important.
Will be measuring with 2x pipe thermometers when close enough to make it worthwhile.
It is the temp difference across flow & return for each rad that I will set ... 11 degree is the typical design range.
However as I did not design or install the system, and looking at standard of work ... I would probably be safe to assume little or no design rules were used.
It is the temp difference across flow & return for each rad that I will set ... 11 degree is the typical design range.
However as I did not design or install the system, and looking at standard of work ... I would probably be safe to assume little or no design rules were used.
Last edited:
Yes, I know what you measure; I'm more interested in what temperature you are using (11C) and how you are measuring it.
11C was the standard for older, non-condensing boilers. Manufacturers of condensing boilers, including Ravenheat, now specify a maximum of 20C. This means the return temperature will be correct for condensing when the flow temperature is 75C.
Not sure about the relevance of that.
Increasing the flow rate will just decrease the differential.
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As mentioned I will be measuring with pipe thermometers ...
"Not sure about the relevance of that." well if wrong diam pipes have been used for part of the run, or pipe layout is incorrect then the flow rate to the rads will not have been well designed ... for example the rad I am having issues with there may be too much flow resistance over long 15mm copper runs for it to work correctly.
The system is more than 20 years old ... but the new Ravenheat was put in during last 5 years and position of boiler moved from a back boiler set up to a wall mounted in the kitchen.
Any of this could mean pipe sizing is not optimum, nor layout ideal.
The standard of installation is poor - for example all horizontal pipe runs are not clipped ... pipes sagging badly, pipes passing through joists not lagged. Vertical pipe runs 1/2 in 1/2 out of plaster.
Several dead loops that can't be drained. (must have fed alternate rads at some point.)
In any event it is what it is.
As to pump ... If the system can not be balanced using speed II, and there are radiators where the temperature
differential is too great, then the pump speed setting would be increased to speed setting III (where it currently is.
The index rad would only reach anywhere near correct F&R temp differential after an Hr .... far too long.
"Not sure about the relevance of that." well if wrong diam pipes have been used for part of the run, or pipe layout is incorrect then the flow rate to the rads will not have been well designed ... for example the rad I am having issues with there may be too much flow resistance over long 15mm copper runs for it to work correctly.
The system is more than 20 years old ... but the new Ravenheat was put in during last 5 years and position of boiler moved from a back boiler set up to a wall mounted in the kitchen.
Any of this could mean pipe sizing is not optimum, nor layout ideal.
The standard of installation is poor - for example all horizontal pipe runs are not clipped ... pipes sagging badly, pipes passing through joists not lagged. Vertical pipe runs 1/2 in 1/2 out of plaster.
Several dead loops that can't be drained. (must have fed alternate rads at some point.)
In any event it is what it is.
As to pump ... If the system can not be balanced using speed II, and there are radiators where the temperature
differential is too great, then the pump speed setting would be increased to speed setting III (where it currently is.
The index rad would only reach anywhere near correct F&R temp differential after an Hr .... far too long.
The problem is be close to an Hr before any stability of Index rad .... which is way wrong. All of the guides on balancing advise up to 1/2Hr to stabilize ... and wait 1/2Hr after any changes.
It hardly gets warm at all in 1/2 Hr .... so system is way off.
I'll have another go on the w/end when I change the rad.
It hardly gets warm at all in 1/2 Hr .... so system is way off.
I'll have another go on the w/end when I change the rad.
Don't know how I missed that.
The only problem with the typical pipe thermometer (e.g. Brannan) is that they are slow and not very accurate. I had a couple which showed a difference of more than five degrees when clipped next to each other on the same pipe. The thermometers need to be 'calibrated' to take account of any errors.
There are very few domestic systems which have been piped completely correctly. Instead of installing the correct size pipe according to the required flow, 22 mm or 28 mm is used for the main backbone and 15mm for all rad drops.
Try balancing with a higher differential, e.g 15C. The easiest way to do that is to reduce the pump speed to 2, but that's not a bad thing as the resistance in the pipes will be reduced due to the lower flow rate.
first thing to check is the balancing as already said
next is to check the return tempreture to the boiler
the reason for this is alot of new combi boilers have an automatic bypass. you have to check your manual for this.
this is why you need a radiator furthest away to have lockshields on to prevent any issues with the valves shutting.
with combi boilers alot of pipe work is changed from the old style with a tank but they leave the old style bypass in the pipework in. this affects flow and you will tell if this is the case by tempreture checking the return to the boiler
i tried balancing but ending up shutting the rads off with still no decent flow to the front room
i had a problem with my front room radiator heating up slowly. the old owner turned off 2 rads so once i reinstanted them the heat wasnt very good
i then changed to a double rad which made it worse. this is when i started investigating. once i took the loop out. you can just cap it my heating has been perfect ever since
next is to check the return tempreture to the boiler
the reason for this is alot of new combi boilers have an automatic bypass. you have to check your manual for this.
this is why you need a radiator furthest away to have lockshields on to prevent any issues with the valves shutting.
with combi boilers alot of pipe work is changed from the old style with a tank but they leave the old style bypass in the pipework in. this affects flow and you will tell if this is the case by tempreture checking the return to the boiler
i tried balancing but ending up shutting the rads off with still no decent flow to the front room
i had a problem with my front room radiator heating up slowly. the old owner turned off 2 rads so once i reinstanted them the heat wasnt very good
i then changed to a double rad which made it worse. this is when i started investigating. once i took the loop out. you can just cap it my heating has been perfect ever since
Since you have a condensing boiler I don't understand why you want an 11 C differential. Usually an installer would aim at about 12-18 C and achieve about 15 C if they were lucky.
Because it is badly installed it probably does not have an auto bypass but you should check to ensure it does not as missetting of that would cause a lack of heat getting to the rads.
Also are you sure that the boiler does have 22 mm tube going to the main parts of the heating system?
Tony
Because it is badly installed it probably does not have an auto bypass but you should check to ensure it does not as missetting of that would cause a lack of heat getting to the rads.
Also are you sure that the boiler does have 22 mm tube going to the main parts of the heating system?
Tony
>The thermometers need to be 'calibrated' to take account of any errors.
I am using in conjunction with a digital thermocouple, so aware of the offset required (about 8 degrees high)
I have been able to improved things.
I am aiming for ~15 degree differential (my 11 degree comment was based on older non condensing boilers )
>Also are you sure that the boiler does have 22 mm tube going to the main parts of the heating system?
I cannot say how the existing pipe layout is under the 1st floor floorboards as it would require a lot of lifting.
What I do know if that the condensing boiler has 22mm flow & return.
These loop around the room the boiler is in (raer of house) and then that pair disappears up to first floor.
I guessing that 22mm does not go to front of the house, and then to 15mm drops to index rad ... but unable at this point to confirm. (maybe I'll convince him to lift boards in a few weeks time)
On last weekend I changed out the Index rad ... to a newer more efficient double convector.
Dropped all of the lockshields on the rads to almost closed and now getting much better performance out of Index rad, will have another go at balancing on next visit.
It is now much better than it was.
Pretty amazed that on every rad ... there are horizontal pipe runs under rad .. none of these had been clipped .. probably due to fact that they were 3-4" off the wall.
Vertical runs also only on clip at bottom of run
2 rads are also on 'dead loops' with no drains tees ... so no way to drain off pipes, I can crack the rad valves .. but due to bends etc .. pipes will remain full.
....shoddy install.
I am using in conjunction with a digital thermocouple, so aware of the offset required (about 8 degrees high)
I have been able to improved things.
I am aiming for ~15 degree differential (my 11 degree comment was based on older non condensing boilers )
>Also are you sure that the boiler does have 22 mm tube going to the main parts of the heating system?
I cannot say how the existing pipe layout is under the 1st floor floorboards as it would require a lot of lifting.
What I do know if that the condensing boiler has 22mm flow & return.
These loop around the room the boiler is in (raer of house) and then that pair disappears up to first floor.
I guessing that 22mm does not go to front of the house, and then to 15mm drops to index rad ... but unable at this point to confirm. (maybe I'll convince him to lift boards in a few weeks time)
On last weekend I changed out the Index rad ... to a newer more efficient double convector.
Dropped all of the lockshields on the rads to almost closed and now getting much better performance out of Index rad, will have another go at balancing on next visit.
It is now much better than it was.
Pretty amazed that on every rad ... there are horizontal pipe runs under rad .. none of these had been clipped .. probably due to fact that they were 3-4" off the wall.
Vertical runs also only on clip at bottom of run
2 rads are also on 'dead loops' with no drains tees ... so no way to drain off pipes, I can crack the rad valves .. but due to bends etc .. pipes will remain full.
....shoddy install.
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