Drayton MA1 not returning under spring pressure, but...

[phmode]

Hi guys.

First post so treat me gently.

I have a really weird problem with a Drayton MA1 mid-position valve and I can't find any reference to this specific problem.

The system is a conventional gravity-fed system with gas condensing boiler, Lifestyle LP522 programmer, Drayton RTS1 room-stat, Honeywell tank-stat, Drayton MA1 MPV and ACL Lifestyle Wiring Centre.

The system has been working perfectly for 14 years until yesterday when the domestic hot water was cold.

I checked the MPV and it was still in the Heating position from the previous evening's central heating demand.

I removed the head unit to check the valve shaft for freedom and the actuator still stayed in the Heating position even though the DHW was set to Off! The shaft of the valve is very free and I can turn it with my fingers.

I turned off the power to the system and immediately the actuator returned to the relaxed, Water, position under spring pressure.

With the head unit removed from the valve body, turning on the system and demanding Heating causes the actuator to move to the H position. Turning down the room stat satisfies the demand and the system shuts down the boiler and the pump but the actuator remains in the H position. Cycling the demand fires the boiler and pump but satisfying the demand with the room-stat has no effect on the actuator which stubbornly remains in H.

However, turning off the system power causes the actuator to return immediately to the W, relaxed, position under spring pressure. Turn on the system power and everything works as it should, until the Heating-only demand is satisfied when the actuator remains in H.

At this point, demanding Hot Water causes the actuator to move to the W position and if the demand for Heating is still there, the actuator moves to the mid-position. (This is counter-intuitive to the problem of no hot water in the morning as when I test the system the actuator moves with hot-water demand even though it had not done so yesterday morning!)

So, it seems as though everything is working normally until there is a demand for Heating only, when, once it is satisfied, the actuator remains in H. This is repeatable!

I have checked the power to the MPV and there is no voltage on the White MPV wire with heating satisfied.

I am at my wits end as the 'logic' just doesn't seem logical. It seems as though it is 'stuck' electrically rather than physically as turning off system power causes the actuator to 'relax' under spring pressure and yet there is no voltage energising it when it is 'stuck' with the system power on!

As always, any inputs greatly appreciated.

Regards, Brian

 

[Gas2Air]

Hi guys.

First post so treat me gently.

I have a really weird problem with a Drayton MA1 mid-position valve and I can't find any reference to this specific problem.

The system is a conventional gravity-fed system with gas condensing boiler, Lifestyle LP522 programmer, Drayton RTS1 room-stat, Honeywell tank-stat, Drayton MA1 MPV and ACL Lifestyle Wiring Centre.

The system has been working perfectly for 14 years until yesterday when the domestic hot water was cold.

I checked the MPV and it was still in the Heating position from the previous evening's central heating demand.

I removed the head unit to check the valve shaft for freedom and the actuator still stayed in the Heating position even though the DHW was set to Off! The shaft of the valve is very free and I can turn it with my fingers.

I turned off the power to the system and immediately the actuator returned to the relaxed, Water, position under spring pressure.

With the head unit removed from the valve body, turning on the system and demanding Heating causes the actuator to move to the H position. Turning down the room stat satisfies the demand and the system shuts down the boiler and the pump but the actuator remains in the H position. Cycling the demand fires the boiler and pump but satisfying the demand with the room-stat has no effect on the actuator which stubbornly remains in H.

However, turning off the system power causes the actuator to return immediately to the W, relaxed, position under spring pressure. Turn on the system power and everything works as it should, until the Heating-only demand is satisfied when the actuator remains in H.

At this point, demanding Hot Water causes the actuator to move to the W position and if the demand for Heating is still there, the actuator moves to the mid-position. (This is counter-intuitive to the problem of no hot water in the morning as when I test the system the actuator moves with hot-water demand even though it had not done so yesterday morning!)

So, it seems as though everything is working normally until there is a demand for Heating only, when, once it is satisfied, the actuator remains in H. This is repeatable!

I have checked the power to the MPV and there is no voltage on the White MPV wire with heating satisfied.

I am at my wits end as the 'logic' just doesn't seem logical. It seems as though it is 'stuck' electrically rather than physically as turning off system power causes the actuator to 'relax' under spring pressure and yet there is no voltage energising it when it is 'stuck' with the system power on!

As always, any inputs greatly appreciated.

Regards, Brian

There is only voltage on the white when heating is demanded. Get a new actuator and make sure the valve spindle is free before fitting.

 

[phmode]

Hi and thanks for the rapid response.

The valve spindle is totally free and the fact that the actuator remains in the H position, even when there is no voltage to the white wire and with the actuator removed from the valve unit, is what is confusing me.

No voltage (because there is no demand) but the actuator remains in H. Turn off system power and actuator returns to W under spring pressure as it should do, but doesn't, when there is no demand.

I don't understand what is stopping the actuator from returning under spring pressure when system power is on even with no demand!

I could buy a new actuator, but I don't understand quite what is wrong in the existing actuator that buying a new one will fix and I don't want to risk wasting £50.

Regards, Brian

 

[Johnmdc]

That is how it is supposed to be. The actuator will stay in the last position it was when the timer shuts off.
So if it was calling for heat when the timer goes to an off time it will stay in the heating position. If gets its live feed from the grey wire which is fed from either the HW off on the clock or satisfied from the cylinder stat.
If you just put the water on on the clock what happens?

 

[Gas2Air]

Hi and thanks for the rapid response.

The valve spindle is totally free and the fact that the actuator remains in the H position, even when there is no voltage to the white wire and with the actuator removed from the valve unit, is what is confusing me.

No voltage (because there is no demand) but the actuator remains in H. Turn off system power and actuator returns to W under spring pressure as it should do, but doesn't, when there is no demand.

I don't understand what is stopping the actuator from returning under spring pressure when system power is on even with no demand!

I could buy a new actuator, but I don't understand quite what is wrong in the existing actuator that buying a new one will fix and I don't want to risk wasting £50.

Regards, Brian

How are you wasting £50? You need a new actuator, end of.

 

[flameport]

So, it seems as though everything is working normally until there is a demand for Heating only, when, once it is satisfied, the actuator remains in H. T

From the description I am not convinced there is any problem here.

The default position of the valve is W, held there by the spring. Power can be applied to the white wire, grey wire or both white and grey.
For hot water only, the valve does not need to move and no power is applied to it.
With power applied to the white wire only, it will move to the mid position for hot water and heating.
For heating only, power is applied to both white and grey, valve moves to H.

When both water and heating are set to Off, power is connected to Grey only.
If the valve was previously at Heating only, the result is the valve being held in that position, so finding the valve at H with no demand after using the heating is normal operation and exactly what you would expect.

No hot water is more likely to be an issue with the programmer or cylinder thermostat.
Hot water On only should be no power applied to grey or white, and the boiler/pump is activated directly by the programmer and thermostat, the valve is not involved at all.

 

[phmode]

Hi John. Many thanks for your response.

So, am I trying to fix a problem that isn't there, (other than not having any hot water yesterday morning)? Perhaps I've never noticed the actuator staying in the H (or the last selected) position before.

As I said, when I turn the water on, the actuator does move to either the mid or W position depending on whether there is demand for Heating as well. In that respect it all works perfectly.

However, whether I have a problem or not, I am still confused.

My (mis)understanding was, assuming we forget about the hot water side of things, that the actuator was motored from the relaxed, W position, to the H position by the demand for Heating and that the actuator then closed back to the W position under spring pressure when that heating demand was satisfied, assuming the timer is still 'on' for heating.

Is this not the case?

From what you say, does the actuator stay in the H position when the demand is satisfied when the timer is still on (as well as when the timer shuts off) and if so, what is keeping it 'actuated' there and thus stopping the spring pressure from returning it to the W position?

Regards, Brian

 

[phmode]

Hi flameport and thanks for your reply. My router is having one of those moments so my post missed your response.

Edited, having been poking around with my multimeter!

So, to answer my own question posed above, it seems that what is holding the actuator in the H position with no demand for Heating, but with the timer 'On', is the 240v on the grey wire from 'HW-OFF' in the programmer!

This then answers my other question about why the actuator returns to W under spring pressure when the system power is turned off. The 240v from the 'HW-OFF' goes away and spring pressure rules!

Guys, I have learned so much about something I always thought I understood! Many thanks to you all!

Regards,

Brian (who is glad he didn't rush out to buy a new actuator and if the hot water problem returns will come back with the answer)

 

[Gas2Air]

Brian, if that's your real name. You have no idea how a simple 3 port actuator works. You do know these have a little circuit board built in that the motor connects to? Of course you do. Just replace it.

 

[phmode]

Why wouldn't Brian be my real name? But Phmode isn't my real name!!

I do know they have a circuit board and very flimsy, but normally reliable, micro-switches but why would I want to go replacing the whole actuator, as you suggested in the first place, or even the circuit board as you now suggest, when the excellent descriptions of correct operation given by both 'Jonhmdc' and 'flameport' show that my actuator was working correctly all along and the only thing at fault was my understanding of its correct operation.

That was why I came here and my misunderstanding has now been corrected thanks to John and flameport!

You did nothing to diagnose the 'fault', were assuring me I needed to buy a new actuator and waste £50, end of! Now you are assuring me I need to change the circuit board! Seeing as you assured me I needed to buy a new actuator, it seems that you are the one who doesn't understand how a simple 3 port actuator works.

Brian (who really is called Brian and who was glad he waited for detailed explanations from those who do understand how a simple 3 port actuator works and who saved him £50 to boot)

 

[oilhead]

How are you checking the hot water operation? If by putting the timer on constant, try setting it a time when you can watch it switch on and make sure it is switching automatically.

 

[phmode]

Hi oilhead.

At the moment, there is nothing wrong with the system, thank goodness. It was a case of putting two and two together and coming up with five. The water was very cool when I showered and so I advanced the timer to heat it up. The boiler was working fine as I had the heating on at the same time.

I checked the MPV to make sure the heat was getting to the coil and it was. However, when I checked the MPV later in the day I noticed that it was in the H position, even though I had turned the heating down on the thermostat. This was the point at which I got thoroughly confused and sought expert advice in here.

As my MPV position indicator is 'hidden' from view, I had never realised that the MPV stayed in the last position demanded by the system and concluded, wrongly, that I had found the cause of the cold shower; assuming that the MPV had not moved when demanded. I had always thought that the MPV only moved to the H position when heating was demanded.

The best advice I got was that my system was working as it should and I am glad to say it is. From those who knew, I learned what it is that holds the MPV in the H position even when there is no demand for heating, the HW-OFF feed from the programmer.

The problem with the cold shower remains a mystery, appears to be a one-off and it has not happened again.

Many thanks again, Brian

 

[Chris_c81]

Apologies for bumping this thread, but it is describing 99% of my current problem.

The problem I am having though is even after the temperature set by thermostat has been reached, and after the scheduled CH OFF, my pump continues to operate, my radiators continue to heat and the temperature continues to increase.

I noticed this last night at around 3am it was still going and the thermostat was reading 25+.

I was ready to go buy a new actuator as I believed this was the problem, however it appears to operate as described in the above discussion.

The MPV actuator is a BGMVSP-23. The control and thermostat is a Hive system. Boiler is a Worcester Greenstar Ri. System is gravity fed open vented system, tanks in the loft and HW cylinder in airing cupboard.

Thanks

Edit: I've just done some more investigating this morning. The problem of the pump continuing to run last night, doesn't appear to occur when I try it now. I unplugged the MPV and it caused the pump to switch off and the valve return to its default W.

Boosted HW MPV stays in W. Boosted CH and MPV moves to H. Turn the boosts off and MPV remains in H and after a short time pump stops.

So I'm confused as to why last night it continued to heat rads.

 

[D_Hailsham]

The pump is wired to the boiler, which controls the pump overrun. (Runs for three minutes after the boiler is switched off.) If the pump was running for longer, the timer may be faulty.

If the boiler is still running after the room thermostat has reached target, then you need to check the room stat and the motorized valve for sticking switch contacts. A multimeter would help.

 

[Chris_c81]

The pump is wired to the boiler, which controls the pump overrun. (Runs for three minutes after the boiler is switched off.) If the pump was running for longer, the timer may be faulty.

If the boiler is still running after the room thermostat has reached target, then you need to check the room stat and the motorized valve for sticking switch contacts. A multimeter would help.

Hi thanks for replying. I've got a multimeter (signalling engineer on the railways) so that side of it is not a problem. But I'm no plumber! So wouldn't really know where to start.

In an update though. I thought I would go pick up a new MPV anyway, replace the old one and see what happens tonight when the CH/HW schedules kick in.

In meantime, I've tested the new MPV and have seen it move from H, to W and to M by demanding separately and together. I've also witnessed it cut the pump out after a short time (the overrun?) following all demands off. So I'm kinda happy that rules out:

MPV
Pump Overrun Timer

Would you agree? Appreciate the help.