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
When the controller turns off the boiler the mid position valves shoul stay where it was last put, so if you last used heating only it blocks (hot water), if you last used hot water it blocks A (Heating), if yo last used both it stays in the mid position. This is effected by powe to the grey lead.
If however all power is cut so there is no voltage on the grey lea either it rests in the hot water only position, obstructing A.
The manual override holds it in the mid position, we use that whe filling the system and getting rid of air locks.
Pau
-- Paul Barker
It seems normal for it to stay put. If you look at the Y-Plan wiring diagram in
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.
I was following up Set Square's point, not the OP's.
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).
Yes I have a Drayton midi also. It stays just as the other poster said engergised if the programmer turns the system off on heating. What a piece of junk, burning electricity all the time when the system is off. Do not buy these things, buy something that spring returns and powers down with the system shutting off.
Someone who doesn't seem to understand that he is replying to a 17 year old post with a reply that indicates that he doesn't understand how his heating system works.
alan_m presented the following explanation :
+1
Looking via the site, it was originally quite an interesting thread, with a knowledgeable post from Andrew Gabriel. What Andrew Failed to realise, or maybe they were not available back then, is that there is a
3-port valve direct replacement for the spring return type, which is called a MOMO (Motor On, Motor Off).MoMo's don't have any springs, instead of returning, the valve rotates to position one way, until it gets to position then stops and the motor is completely powered down once in position.
Much less strain on the actuator due to no springs, no motor powered up much of the time, so less internal heat generated and potentially a much more reliable valve, plus it is a direct electrical replacement for the spring return type.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.