One on One Advice - Y Plan Behaviour

[LoweLight]

Is anyone available, for a fair fee, to walk/talk me through diagnosing some behaviour that I think is incorrect for my system? In covid-times I want to avoid calling someone in if I can. I am quite competent with a great many topics, but being new-ish to the UK I'm not intimately familiar with Y-Plan combi boiler gravity fed systems so I want to talk to someone that is really in the know, can guide me through some diagnosis steps, and see if I can fix it myself.

Here's a summary:
Greenstar Ri boiler
Davtron MA1 electronic valve actuator
Honeywell ST9400C programmer/timer

Last year this was all working correctly but at the start of this season I noticed the valve actuator wasn't moving according to the usual inputs from the room thermostat; a call for heat would not move the actuator to the CH (B) side. The diverter stays in water heat (A) all the time.
The pump ALWAYS runs as far as I can see unless I shut off the heat and water heat on the timer, AND if I turn down the thermostat on the tank.
If there's a call for central heat, the diverter won't move. I can push the lever on the side to the middle position where it stays until the room heats up and the thermostat shuts it off. The valve then moves to the water heat (A) position and stays there until I actuate the lever manually again.

If I turn off water heat on the programmer and actuate the lever manually (with room thermostat calling for heat), it will automatically move from the middle position over to the CH (B) side. Room warms up, call for heat turns off, valve goes to A position automatically and the cycle restarts.

In all cases for me to get heat to the rads, I have to actuate the valve manually.

I replaced the motor in the actuator today to no effect. We've found the thermostat on the tank must be cranked all the way up to have enough hot water for a family of 5's showers. Because of a power outage yesterday and me replacing the motor in the actuator valve today, I can safely say the system has been turned off and back on again.

I've googled this and a lot of the forums talk about PCB's in boilers, bad wiring, stuck divertor valves/actuators.. I'd just like to isolate the issue and if it's something I have to call someone in for, so be it but I want to fix it myself. I think about the only thing I CAN'T do is gas work, not certified. But I'm competent with plumbing and electricity.

 

[Gasguru]

You have your mid-pos valve ports mixed up....Port B is for DHW and Port A is for heating.

You must have 3 control wires from the cylinder thermostat (and maybe an earth if required).

The cylinder stat should normally be positioned a 1/4 of the way up from the base of the cylinder and in good contact with the surface and set to 60 degrees.

Start by checking all the wiring is correct and if necessary using a multimeter to confirm correct cabling...a surprising number of Y plans never work properly due to incorrect wiring.

For starters look at the Drayton MA1 manual but you will need to check your own cylinder, room thermostat and programmer for the appropriate terminals.

https://www.google.co.uk/url?sa=t&r...%20Guide.pdf&usg=AOvVaw0DZFpLdcYhtMOGISqgCouD

Be aware the Draytons have had many design faults over the years...the most common being the 2 return spring lugs can shear off preventing the spindle from returning to the DHW position.
The springs can be hooked back on through the base plate. Also check the spindle is free to turn by uncliping the actuator.

The pump should be wired directly to the boiler...the boiler determines when to run the pump.

 

[terryplumb]

If the system worked fine a year ago ,the wiring then would have been ok ,so you only need to check any wiring that you have worked on.
Can you post pics of the wiring centre ?

 

[LoweLight]

I can post pics, but haven't worked on any wiring. It's a matter of working last winter, staying on all summer except the room thermostat was turned down, and then turning it back up when it started to get cooler here but found the valve wasn't actuating. I'll look into posting a wiring pic tomorrow.

 

[ericmark]

I will guess, and can only guess, that a micro switch has stuck inside the three position valve head. But you say you have changed the head.

So the boiler is powered direct from the tank thermostat and the valve should not move at all for DHW only.
With central heating only the valve moves all the way, and the boiler is powered from orange wire out of valve head.
For both DHW and CH the boiler is powered from the tank thermostat and the valve travels half way.

 

[terryplumb]

I

I will guess, and can only guess, that a micro switch has stuck inside the three position valve head. But you say you have changed the head.

So the boiler is powered direct from the tank thermostat and the valve should not move at all for DHW only.
With central heating only the valve moves all the way, and the boiler is powered from orange wire out of valve head.
For both DHW and CH the boiler is powered from the tank thermostat and the valve travels half way.

The " head" ( actuator ) has not been replaced . Only the motor Eric.

 

[ericmark]

Reading again I think the tank thermostat may be the cause, some where I have a plan of how the valve works I will return when I find it.

 

[LoweLight]

I will guess, and can only guess, that a micro switch has stuck inside the three position valve head. But you say you have changed the head

I changed out the synchron motor in the head, the PCB etc are unchanged.. I wondered if there was something in the remains of the unit that might not be working right.

 

[ericmark]

Found it, grey wire comes from the tank thermostat and white from room thermostat, if the grey is not energised when the storage tank is hot then that would explain why CH does not work.

 

[ericmark]

I assume you have a Y plan diagram

also note a HW off at the time controller (programmer) so unless connected central heating will not work with DHW off.

 

[LoweLight]

Reading again I think the tank thermostat may be the cause, some where I have a plan of how the valve works I will return when I find it.

I've wondered same, the tank thermostat, while held fairly tight to the tank, can be pulled out a bit AND I'm not certain if it's in the correct position. What I mean is that it can be rotated a full 360. A honeywell L641A1005, the dial on the front can spin a full 360. We did have a tech here last year that messed with the system and I'm not convinced he knows what he's doing, my point being that he left here with the tank thermostat cranked past 80, pointing straight down. I've attached a manual for a newer version here but it looks similar and illustrates my point. So while it's marked "min" here, it's maxed out, rotated clockwise past 80..

How does one test these, maybe I just need to rotate it to the correct position. if I put it down at 80, I generally don't seem to have enough hot water.

 

[LoweLight]

How does one test these, maybe I just need to rotate it to the correct position. if I put it down at 80, I generally don't seem to have enough hot water.

Found my answer here
https://www.diynot.com/diy/threads/how-to-test-honeywell-l641-cyl-stat.311552/
Tomorrow's project

 

[ericmark]

I would find where the tank thermostat connects to wiring centre, disconnect it and link C to 2 and try, however if you look at plan grey, 2, and DHW off are all connected together, so if wired correct and tank thermostat faulty, turning off DHW at the programmer should mean you get CH even if tank thermostat faulty.

 

[ericmark]

I have only worked on Y plan once, I tried using a meter, but did not have the plan of inside the activator, and the diodes and resistors resulted in unexpected readings.

 

[LoweLight]

As promised, here is a main view that I labeled to assist.. It doesn't appear that the installer used a layout that matches the diagrams above, and I don't have a dedicated mains feed; it must be coming up from the boiler or something but there's no cable from the mains panel to this closet.

The only thing that seems to conform is the wire colours from the diverter valve, and that may be able to deduce if the connections are correct but I doubt all the information is there, and I would understand how difficult it is to check through a picture. I'm going to tinker a bit today.