Stuck bypass and balancing system.
- Thread starter wobbly2
- Start date
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Very. If you have a modern boiler you'll be struggling to heat the house (too much hot flow going thru the bypass and straight back). Needs sorting
Ok thanks.
The boiler is a Glow Worm 30CXI, which is a bit old now and I understand weren't very good when new. We're hoping to change it in the summer/autumn but need it to last 'til then. We're fairly certain that it is oversize for the size of house (66sqm bungalow with 6 rads and a mini bathroom rad). It seemed to be cycling too frequently when the house was warming up (presumably) with TRV's fully open.
I could not get the system return temp low enough for the boiler to condense, hence the question about balancing. We've been running the boiler at between 60-65'c to try but, although it does heat the house (20'c), it has to turned on early to have a chance.
I've read that running the system at a low temp for longer is better as this will more likely to get the boiler condensing for longer but I've also read this is a load of codswallop.
Would I be right in thinking that if the boiler's auto bypass is permanently open then running it at a low temp will not help much with regard to it condensing?
What would be a typical cost to get the bypass replaced?
The boiler is a Glow Worm 30CXI, which is a bit old now and I understand weren't very good when new. We're hoping to change it in the summer/autumn but need it to last 'til then. We're fairly certain that it is oversize for the size of house (66sqm bungalow with 6 rads and a mini bathroom rad). It seemed to be cycling too frequently when the house was warming up (presumably) with TRV's fully open.
I could not get the system return temp low enough for the boiler to condense, hence the question about balancing. We've been running the boiler at between 60-65'c to try but, although it does heat the house (20'c), it has to turned on early to have a chance.
I've read that running the system at a low temp for longer is better as this will more likely to get the boiler condensing for longer but I've also read this is a load of codswallop.
Would I be right in thinking that if the boiler's auto bypass is permanently open then running it at a low temp will not help much with regard to it condensing?
What would be a typical cost to get the bypass replaced?
Long as the bypass is reasonably accessible replacement should be a £100-£150 sort of job (depends where you are in the country & how much faff is involved getting to it).
What makes you think the bypass is permanently open?
65 is a bit high for condensing. Lower flow temp is better BUT if your rads are older than the boiler and were sized for higher flow temp they're going to struggle to heat the house at condensing temperatures.
Boiler cycling could be due to inadequate pump, thermostat fighting trvs, sludged up pipework (not microbore is it).
What makes you think the bypass is permanently open?
65 is a bit high for condensing. Lower flow temp is better BUT if your rads are older than the boiler and were sized for higher flow temp they're going to struggle to heat the house at condensing temperatures.
Boiler cycling could be due to inadequate pump, thermostat fighting trvs, sludged up pipework (not microbore is it).
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When checking that I had properly closed the integral fill loop tap, I found the bypass pipe was hot. (The pipe runs along the front of the boiler just above its open bottom and is touchable when topping up the system pressure using the integral filling loop tap). I checked the filling loop tap because the system pressure had unexpectedly risen after topping it up and I thought I hadn’t closed the tap properly but it was closed.
I didn’t expect the bypass pipe to be hot because the heating had not been on very long and was not up to temperature. The TRV’s should not have been closed or closing. Plus, the hall radiator has its TRV head removed and the bathroom radiator is the heat leak with no TRV.
Wondering if a permanently open bypass could thwart my attempts to balance the system and get a condensing return temperature (less than 55’C), I checked the pipe’s temperature during several cycles of the system heating up and cooling down; and found it followed that of the flow pipe. I rechecked it with all TRV heads removed with the same result and also with all lock-shields fully open.
The radiators are: ( using Panel Radiator Output Calculator | Castrads)
· Bed 2 - 1040 watt older single panel with TRV
· Hall - 1720 watt older double panel with TRV head removed
· Bed 1 - 3097 watt older double panel with TRV
· Lounge - 3441 watt older double panel with TRV
· Bathroom - 260 watt newer single convector with no TRV
· Kitchen - __736 watt newer single convector with TRV
10294 watts total
The house is a bungalow of approx. 66 sq. metres. The boiler has a fixed speed pump and max output of 24.7kW in CH mode, modulating down to 5 or 6 kW. I’ve been advised that the output of the boiler may be too high for the heating load and the fixed speed pump circulates the water to fast for good heat transfer from the radiators, hence, the high return temperatures; which presumably is exacerbated if the bypass is stuck open.
Even with the boiler set to 60/65’C, the return temerature from the radiators rises very quickly to within 3 or 4’C of the flow with all radiators getting hot and without any cold spots. It's the same with all TRV heads removed (the valve pins move freely up and down).
The TRV for the hall, where the wall thermostat is located, is removed to stop the two fighting each other.
The system was flushed for 3 weeks back in the summer and each rad gets hot quite quickly, so I'm hoping the pipework is not sludged up.
Pipework is 22mm from boiler to branches then 15mm to radiators, except Bed2 and Bathroom which are on the same common 15mm branch and are the slowest to heat up.
I didn’t expect the bypass pipe to be hot because the heating had not been on very long and was not up to temperature. The TRV’s should not have been closed or closing. Plus, the hall radiator has its TRV head removed and the bathroom radiator is the heat leak with no TRV.
Wondering if a permanently open bypass could thwart my attempts to balance the system and get a condensing return temperature (less than 55’C), I checked the pipe’s temperature during several cycles of the system heating up and cooling down; and found it followed that of the flow pipe. I rechecked it with all TRV heads removed with the same result and also with all lock-shields fully open.
The radiators are: ( using Panel Radiator Output Calculator | Castrads)
· Bed 2 - 1040 watt older single panel with TRV
· Hall - 1720 watt older double panel with TRV head removed
· Bed 1 - 3097 watt older double panel with TRV
· Lounge - 3441 watt older double panel with TRV
· Bathroom - 260 watt newer single convector with no TRV
· Kitchen - __736 watt newer single convector with TRV
10294 watts total
The house is a bungalow of approx. 66 sq. metres. The boiler has a fixed speed pump and max output of 24.7kW in CH mode, modulating down to 5 or 6 kW. I’ve been advised that the output of the boiler may be too high for the heating load and the fixed speed pump circulates the water to fast for good heat transfer from the radiators, hence, the high return temperatures; which presumably is exacerbated if the bypass is stuck open.
Even with the boiler set to 60/65’C, the return temerature from the radiators rises very quickly to within 3 or 4’C of the flow with all radiators getting hot and without any cold spots. It's the same with all TRV heads removed (the valve pins move freely up and down).
The TRV for the hall, where the wall thermostat is located, is removed to stop the two fighting each other.
The system was flushed for 3 weeks back in the summer and each rad gets hot quite quickly, so I'm hoping the pipework is not sludged up.
Pipework is 22mm from boiler to branches then 15mm to radiators, except Bed2 and Bathroom which are on the same common 15mm branch and are the slowest to heat up.
Don't trust the taps on your filling loop- it it's the type with a flexi and 2 taps, close them both then disconnect one end of the loop.
How long is the bit of tube (with bypass) between flow and return- copper is a good conductor of heat,
How long is the bit of tube (with bypass) between flow and return- copper is a good conductor of heat,
The integral filling loop has a copper tube with a plastic tap on one end and a (low pressure zone?) valve on the other, see library photo below.
The bypass pipe is copper and looks to be about 300mm long that goes from the left-had side of the boiler to somewhere in the middle. It's a bit difficult to see exactly looking up through the bottom as I can't see its entire length. I did find a clear picture on Google that showed the bypass and fill tap but didn't save it and can't find it again but I did find the exploded diagram below. In the picture the pipe ran from a black plastic ? block on the left-hand side to another black plastic? block towards the middle. I think the bypass is items labelled 86 and 116 in the diagram. I measured the pipe in several positions along the lower section of the pipe.
I understand that copper is a good conductor of heat and I guess your thinking that I was measuring heat transfer along the pipe from where connects to the bypass valve but the pipe's temperature mirrors that of the flow pipe almost instantly, most notably when the boiler is switched on from cold.
The bypass pipe is copper and looks to be about 300mm long that goes from the left-had side of the boiler to somewhere in the middle. It's a bit difficult to see exactly looking up through the bottom as I can't see its entire length. I did find a clear picture on Google that showed the bypass and fill tap but didn't save it and can't find it again but I did find the exploded diagram below. In the picture the pipe ran from a black plastic ? block on the left-hand side to another black plastic? block towards the middle. I think the bypass is items labelled 86 and 116 in the diagram. I measured the pipe in several positions along the lower section of the pipe.
I understand that copper is a good conductor of heat and I guess your thinking that I was measuring heat transfer along the pipe from where connects to the bypass valve but the pipe's temperature mirrors that of the flow pipe almost instantly, most notably when the boiler is switched on from cold.
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