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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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Central Heating Mid-position valve - should it return using spring
My mid-position valve stays powered up in the Heating position even if
nothing is demanding. Is this correct, or should it return to the Water position using the spring return (like it does if you completly power down the whole central heating system)? Cheers Paul |
#2
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If however all power is cut so there is no voltage on the grey lead either it rests in the hot water only position, obstructing A. The manual override holds it in the mid position, we use that when filling the system and getting rid of air locks. Paul |
#3
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In an earlier contribution to this discussion,
wrote: My mid-position valve stays powered up in the Heating position even if nothing is demanding. Is this correct, or should it return to the Water position using the spring return (like it does if you completly power down the whole central heating system)? Cheers Paul It seems normal for it to stay put. If you look at the Y-Plan wiring diagram in http://content.honeywell.com/uk/homes/systems.htm you'll see that one or other wire to the valve is receiving power under just about every condition. The acid test is to remove all power from the heating system by turning it off at the FCU (not the programmer). *Then* you should hear the spring return taking it back to the HW position. -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
#4
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In article ,
"Set Square" writes: In an earlier contribution to this discussion, wrote: My mid-position valve stays powered up in the Heating position even if nothing is demanding. Is this correct, or should it return to the Water position using the spring return (like it does if you completly power down the whole central heating system)? Cheers Paul It seems normal for it to stay put. If you look at the Y-Plan wiring diagram in http://content.honeywell.com/uk/homes/systems.htm you'll see that one or other wire to the valve is receiving power under just about every condition. The acid test is to remove all power from the heating system by turning it off at the FCU (not the programmer). *Then* you should hear the spring return taking it back to the HW position. If it was in mid-postion when you remove power, then it is OK for it to either stay there or return to the hot water position. Mid position is normally held by feeding the synchronous motor with a DC supply which locks its rotor. When power is removed, you can be left with residual magnetism in the field yoke caused by the DC supply having slightly magnetised it, which can continue to lock it into mid-position. Often a slight tap in this state or touching the indicator lever is enough for the spring to overcome this temporary mangetism. When the unit is powered and needs to return to the hot water position, a tiny AC current is leaked through the field winding via a 270k resistor which is just enough to kill this temporary residual magnetism in the field yoke and allow the spring return to operate. -- Andrew Gabriel |
#5
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"Andrew Gabriel" wrote in message ... In article , "Set Square" writes: In an earlier contribution to this discussion, wrote: My mid-position valve stays powered up in the Heating position even if nothing is demanding. Is this correct, or should it return to the Water position using the spring return (like it does if you completly power down the whole central heating system)? Cheers Paul It seems normal for it to stay put. If you look at the Y-Plan wiring diagram in http://content.honeywell.com/uk/homes/systems.htm you'll see that one or other wire to the valve is receiving power under just about every condition. The acid test is to remove all power from the heating system by turning it off at the FCU (not the programmer). *Then* you should hear the spring return taking it back to the HW position. If it was in mid-postion when you remove power, then it is OK for it to either stay there or return to the hot water position. Mid position is normally held by feeding the synchronous motor with a DC supply which locks its rotor. When power is removed, you can be left with residual magnetism in the field yoke caused by the DC supply having slightly magnetised it, which can continue to lock it into mid-position. Often a slight tap in this state or touching the indicator lever is enough for the spring to overcome this temporary mangetism. When the unit is powered and needs to return to the hot water position, a tiny AC current is leaked through the field winding via a 270k resistor which is just enough to kill this temporary residual magnetism in the field yoke and allow the spring return to operate. I don't think you have answered what the OP asked Andrew - It seems to me he was asking if the valve would (should) stay in the fully powered up i.e. open to heating position when the clock, thermostat, etc turns off. The answer is yes it does stay in that position unless a water "call" is applied or as you suggested ALL power is turned off at the isolator. It is a defect in the design of the Y plan as it can lead to the motor spending very long periods energised although it has been a known problem for many years and it is unlikely to be modified now. I prefer to install S plan for just this reason. |
#6
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In article ,
"John" writes: I don't think you have answered what the OP asked Andrew - It seems to me he I was following up Set Square's point, not the OP's. was asking if the valve would (should) stay in the fully powered up i.e. open to heating position when the clock, thermostat, etc turns off. The answer is yes it does stay in that position unless a water "call" is applied or as you suggested ALL power is turned off at the isolator. It is a defect in the design of the Y plan as it can lead to the motor spending very long periods energised although it has been a known problem for many years and it is unlikely to be modified now. I prefer to install S plan for just this reason. I'm not actually familiar with the common 'plans'. My mid position valve and boiler demand for heat are driven by a computer program of my own design. I did however have to sit down and carefully work out how to drive a mid position valve in order to do this, and it wasn't as obvious as it seemed at first. I talked with one of the manufacturers who were extremely helpful and put me in direct contact with one of their valve designers, who explained the residual magnetism issue (I kept having the valve stick in the middle position until I discovered I had to degauss the yoke). -- Andrew Gabriel |
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