Heating/Hot water controller query

[electroman68]

Hi There,

My mum has the following setup.

Potterton 40e boiler
Honeywell Controller (I think it's an ST699)
Drayton MA1 mid position actuator
Drayton room thermostat (non digital)

It used to be possible to have the domestic hot water set to once or twice and the heating set to constant and then operated from the room stat. This configuration worked fine.

However, within the past year she had to have a new mid position valve fitted (model shown above) and the installer had issues with the wiring configuration and had to make a few calls back to base.

The result is that now she has to have both heating and hot water switched to constant on the controller in order for the heating to work. If the hot water is switched to anything other than constant then the boiler will not fire up to provide heating, unless the hot water is set to once or twice and it is within the time slot for these to work.

I'd just like your thoughts on whether this sounds right?

The real issue here is that my mums gas bill has been escalating recently and we're wondering whether it is because both hot water and heating are set to constant. She lives on her own in a small bungalow and doesn't use a lot of domestic hot water, only enough for a wash, shower and washing up, so having water on constant all of the time seems excessive.

Anyway, i'd be interested to know your thoughts.

Thanks in advance.
Rob.

 

[flameport]

I'd just like your thoughts on whether this sounds right?

No.

The person who installed the replacement actuator has got the wiring wrong.

 

[ianmcd]

As above it is not wired correctly

 

[electroman68]

Hi both, thanks for your replies. That's interesting as there was a small leak at one of the valve joints last week and so my mum called an heating engineer out. Whilst there she explained to him about the heating controller issue and he said that it's probably because there aren't enough conductors in the cable to the controller to enable connection of the 'HW off' to the valve.

I did further tests since my last post and this is what I found.

1. HW + CH set to constant on controller = valve in 'H' position
2. HW once and CH constant = valve in 'M' position
3. HW constant and CH once = valve in 'W' position

Now, I appreciate that the valve will be wherever it was after the last demand for CH or HW, but shouldn't the valve move to 'M' if both CH and HW are set to constant, or does this depend on whether the hot water in the cylinder has already reached temperature? Also, regarding point 2 above, shouldn't the valve move the the 'H' position?

Whilst not being an expert in heating systems (hence my post here) I am an electronics engineer so would be happy to take some voltage measurements at various points if it may help troubleshoot the issue.

Thanks again for your replies so far.

Rob.

 

[ianmcd]

the engineer is correct it is the HW off wire that moves the actuator to the H position if CH demanded, the HW off from the programmer and the HW satisfied from the cyl stat both do this, some makes the valve will make a clicking noise when the HW off has not been connected

 

[electroman68]

Thanks Ian. I may take a look to see how many wires are in the cable from the valve to controller to see if this is the reason that 'HW OFF' has not been connected, if indeed it isn't actually connected when I take a look. I have been advise that options may be to replace the cable or possibly change the controller to one that allows for more control over heating water and radiators independently.

 

[ianmcd]

you shouldnt need to change the cable, more likely he just hasnt connected the wires correctly, if it worked before he changed the valve then you have enough cores for it to be wired correctly, post some pics of the wiring centre and the programmer back plate and we will be able to advise you, also with the programmer if you have the HW set to off and just slide the CH to on does the HW on light also come on ?

 

[electroman68]

Hi Ian. Here are images of the wiring centre and controller backplate. The wiring is a bit of a mess so hope you're able to make sense of the connections.

With regards to your question, if I set the HW to off and the CH to constant the HW light does not illuminate. Incidentally, if the CH is set to constant then the CH light illuminates (as expected) but if the room stat is then turned up the boiler doesn't fire up.

 

[electroman68]

Just for reference, the black cable coming into junction box comes from the mid point actuator and the white cable comes from the cylinder stat.

 

[ianmcd]

yes it is as we advised, the black cable in the junction box has a grey wire, can you see where that goes to ? it should be connected to terminal 7 on the programmer and also to HW satisfied on the cylinder thermostat, that is your problem

 

[electroman68]

Hi Ian. Ah, that's interesting and, as you say, that sounds like the culprit. I'm not at my mums at the moment but will be popping over at the weekend so will check where the grey wire goes. As you can see, there certainly doesn't appear to be anything connected to terminal 7 on the controller at the moment anyway.

Thanks again for your help with this, it's most appreciated. I'll update with info regarding the grey wire in due course.

 

[ianmcd]

that is definitely your problem, come back and let us know how you get on

 

[electroman68]

Hi Ian. I took a closer look at the wiring centre on Saturday and noticed the following.

NO on cylinder stat (black wire) connects to Mid Point Actuator grey wire. Grey wire doesn't connect to anything else.
NC on cylinder stat (grey wire) connects to Mid Point Actuator red wire and also goes off to controller, although I'm not sure exactly what terminal.
COM on cylinder stat goes off to controller, but again I'm unsure of where this connects without investigating further.

There is currently no wire connected to terminal 7 on the controller, or indeed terminal 4.

I hope this is sufficient info for you to confirm diagnosis of the issue, but please let me know if you'd like me to check anything else.

Regards.

 

[electroman68]

Hi again. My mum now thinks that the wiring in the controller was not altered when the new mid point actuator was fitted. My question is therefore, how could the system ever have worked correctly? It did though before the valve was replaced. Now, there are two possible theories.

1. The controller wiring was changed but for some reason my mum wasn't aware of it. Seems unlikely as my mum is convinced the engineer was only working in airing cupboard where valve is. Controller is near boiler in kitchen.

2. The previous valve had somehow been wired up to allow heating to work when set on constant and hot water set to timed.

This all seems a bit strange, hmmmm........

Thanks for all your help so far.