W
wilhelm
well, i just read the first post and he described . w plan.
thats all.
thats all.
Weird Central Heating Problem
- Thread starter PhilWis
- Start date
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W
wilhelm
well thats ok.
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Pretty sure it's not a boiler flow temp issue. Turned boiler stat right up but still doesn't seem to turn pump off when just on HW or indeed divert flow to rads when both HW or CH are on.
I know nothing about these things but I reckon there must be wiring fault.
I know nothing about these things but I reckon there must be wiring fault.
Also looks like a wiring fault to me. Shouldn't be too difficult to sort out.
You need to check for voltage on the 'orange' 'white' and 'grey' wires under the various conditions.
I would start by turning everything off including the electric supply to the system, this allows the motorised valve to return to the start position, which is the HW position. (The valve can be heard moving).
Now turn the HW on, this supplies electric to the input side of the cylinder stat. The cylinder stat has two output terminals. ('Not satisfied' and 'satisfied') One output goes to the orange wire on the MV whilst the other output goes to the grey wire on the MV.
Turning up the cylinder stat 'Not satisfied' will supply electric to the 'orange wire', carry out test to verify this is happening.
Now turn the cylinder stat down (or let water heat up) to get the 'satisfied' position. carry out test to veryify there is now a voltage on the grey wire of the MV and no voltage on the 'orange'
Up to now the MV has not moved so now turn off the HW. The HW has two outputs 'HW on' and 'HW off'. The HW off terminal is needed to supply electric to the grey wire because the normal route through the cylinder stat has been cut off when the HW was turned off. In this positon there should still a voltage on the 'grey' wire' it's just that it'd fed from a different source. So this can be checked .
Now with HW off, turn room stat down and turn.CH on.The input to the room stat will be live and can be checked if desired. However by now turning up the room stat it will supply electric to the 'white wire' on the MV
This can also be checked. Also it will drive the motor and turn the valve from the start position through the mid point and continue to the final position. from here there are 3 possabilities, You may switch the CH off, or it may become satisfied and the MV stays put but boiler no longer operates or you may switch HW on in which case voltage on 'grey' wire is removed which allows MV to drop back to mid position.
Hope you find it useful.
You need to check for voltage on the 'orange' 'white' and 'grey' wires under the various conditions.
I would start by turning everything off including the electric supply to the system, this allows the motorised valve to return to the start position, which is the HW position. (The valve can be heard moving).
Now turn the HW on, this supplies electric to the input side of the cylinder stat. The cylinder stat has two output terminals. ('Not satisfied' and 'satisfied') One output goes to the orange wire on the MV whilst the other output goes to the grey wire on the MV.
Turning up the cylinder stat 'Not satisfied' will supply electric to the 'orange wire', carry out test to verify this is happening.
Now turn the cylinder stat down (or let water heat up) to get the 'satisfied' position. carry out test to veryify there is now a voltage on the grey wire of the MV and no voltage on the 'orange'
Up to now the MV has not moved so now turn off the HW. The HW has two outputs 'HW on' and 'HW off'. The HW off terminal is needed to supply electric to the grey wire because the normal route through the cylinder stat has been cut off when the HW was turned off. In this positon there should still a voltage on the 'grey' wire' it's just that it'd fed from a different source. So this can be checked .
Now with HW off, turn room stat down and turn.CH on.The input to the room stat will be live and can be checked if desired. However by now turning up the room stat it will supply electric to the 'white wire' on the MV
This can also be checked. Also it will drive the motor and turn the valve from the start position through the mid point and continue to the final position. from here there are 3 possabilities, You may switch the CH off, or it may become satisfied and the MV stays put but boiler no longer operates or you may switch HW on in which case voltage on 'grey' wire is removed which allows MV to drop back to mid position.
Hope you find it useful.
Thanks Mandate.
Not sure I can do this myself but I'll print off your instructions and see if I can get someone to run through them.
+++++++++++++++++++++++++++++++++
Mandate,
The wiring diagram I have refers to
COM
CALL
SAT
against the cylinder thermostat.
+++++++++++++++++++++++++++++
and...............
Can the test be done with an ordinary mains test screwdriver?
If SAT = satisfied then what are the others short for?
________________________
moderator
please note 10a which is here
Not sure I can do this myself but I'll print off your instructions and see if I can get someone to run through them.
+++++++++++++++++++++++++++++++++
Mandate,
The wiring diagram I have refers to
COM
CALL
SAT
against the cylinder thermostat.
+++++++++++++++++++++++++++++
and...............
Can the test be done with an ordinary mains test screwdriver?
If SAT = satisfied then what are the others short for?
________________________
moderator
please note 10a which is here
PhilWis,
This table, which summarises the information provided in Mandate's post above, may be of help when checking the voltages of the wires to the 3-Port valve:
You may be able to do the check with just a mains test screwdriver. However, when the valve is in its mid-position the grey wire will be at a reduced voltage (somewhere between 90 and 150 Volts). This might be difficult to detect as a change in brightness of the screwdriver's neon (compared to that at 240 Volts), so a cheap multimeter would be a better option.
If the wiring is correct, then the problem could be due to the CH and DHW flows being out of balance.
Assuming that your hot water cylinder is at least as old as the previous boiler, its coil is likely to have a low flow resistance, compared to that of a modern high recovery heating coil, and may even have been designed for use in a gravity fed hot water system. If that is the case, the hot water will pass through the coil quickly, give up very little heat and return to the boiler almost as hot as it left. Many new boilers modulate their gas rate in direct proportion to the heating demand. A high return temperature is interpreted as a lack of demand and, consequently, the boiler's output is reduced. If your boiler has a modulating gas valve then, whenever there's a demand for hot water, it may be operating at minimum heat output.
Installing a gate valve (lock shield) inline with the coil would allow the CH and DHW flows to be balanced.
This table, which summarises the information provided in Mandate's post above, may be of help when checking the voltages of the wires to the 3-Port valve:
You may be able to do the check with just a mains test screwdriver. However, when the valve is in its mid-position the grey wire will be at a reduced voltage (somewhere between 90 and 150 Volts). This might be difficult to detect as a change in brightness of the screwdriver's neon (compared to that at 240 Volts), so a cheap multimeter would be a better option.
If the wiring is correct, then the problem could be due to the CH and DHW flows being out of balance.
Assuming that your hot water cylinder is at least as old as the previous boiler, its coil is likely to have a low flow resistance, compared to that of a modern high recovery heating coil, and may even have been designed for use in a gravity fed hot water system. If that is the case, the hot water will pass through the coil quickly, give up very little heat and return to the boiler almost as hot as it left. Many new boilers modulate their gas rate in direct proportion to the heating demand. A high return temperature is interpreted as a lack of demand and, consequently, the boiler's output is reduced. If your boiler has a modulating gas valve then, whenever there's a demand for hot water, it may be operating at minimum heat output.
Installing a gate valve (lock shield) inline with the coil would allow the CH and DHW flows to be balanced.
CH4,
Thanks for the info. I will do a voltage check when I get a spare 5 mins.
I had the cylinder replaced at the same time.
The boiler is a Glow-worm 24hxi. From what the installer said, it does indeed 'modulate'. When it fires up one can here the whoosh but this soon falls back to an almost silent burn. Only when the CH is on does the boiler really make any real sound or noise.
Thanks
Thanks for the info. I will do a voltage check when I get a spare 5 mins.
I had the cylinder replaced at the same time.
The boiler is a Glow-worm 24hxi. From what the installer said, it does indeed 'modulate'. When it fires up one can here the whoosh but this soon falls back to an almost silent burn. Only when the CH is on does the boiler really make any real sound or noise.
Thanks
CH4 said:PhilWis,
You may be able to do the check with just a mains test screwdriver.
If the wiring is correct, then the problem could be due to the CH and DHW flows being out of balance.
Assuming that your hot water cylinder is at least as old as the previous boiler, its coil is likely to have a low flow resistance, compared to that of a modern high recovery heating coil, and may even have been designed for use in a gravity fed hot water system. If that is the case, the hot water will pass through the coil quickly, give up very little heat and return to the boiler almost as hot as it left. Many new boilers modulate their gas rate in direct proportion to the heating demand. A high return temperature is interpreted as a lack of demand and, consequently, the boiler's output is reduced. If your boiler has a modulating gas valve then, whenever there's a demand for hot water, it may be operating at minimum heat output.
Installing a gate valve (lock shield) inline with the coil would allow the CH and DHW flows to be balanced.
I have checked the wiring in accordance with the diagram with an electrical screwdriver. I picked up voltage as per the diagram so it doesn't seem to be a wiring fault.
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