Honeywell three port motorised valve - replace the whole thing? And other questions...

[Plumb Line]

Hi again

I'm on a roll with the plumbing questions today! So here's query #2...
We've not used our hot water for quite some time, and it now doesn't work. From what I can gather based on what I've learnt in the last hour or two, I think the problem is with the 3 port motorised valve. When just hot water is selected at the controls, we don't get hot water, but we do get hot radiators. Just to be clear, that's with hot water selected to continuous, heating off, and the heating thermostat turned right down. Up in the airing cupboard, I can feel - at the valve - that the pipe going from point B to the cylinder stays cold, while the pipe from point A warms up. The little lever bit doesn't move and stays in auto position. So presumably the valve for one reason or another is stuck and no matter what the controls tell it to do, only port A is open. Does that sound about right?

If so, I wondered if anyone could help with the following please?

1. We've got some major plumbing work coming up soon, which will require a full drain down. As such, would it be worth changing the whole unit? I've seen some try just changing the motor, others just the power head. But whilst drained down is it worth spending the extra and just replacing the whole thing?

2. My unit is a Honeywell V4073A1088. The one you tend to see most is the V4073A1039. I looked into it and all I could find is the former is 28mm and the latter 22mm. I presumed that related to the pipes feeding it, but does it? The reason I ask is because I have 22mm pipes and yet mine is supposedly the 28mm version. Which has me scratching my head!

3. One forum thread I was reading stated: "“It explains why you can't use a mid position for your HW and RADS and then add a two port for extra rads or UFH.” Is that correct? Is it a blanket statement? Later in the year we are looking to have UFH installed elsewhere in the house, so I'd be interested to know if it would need changing again at some point. For reference, the quote comes from here:

https://community.NoLinkingToThis/threads/motorised-valves-that-little-lever.173511/

4. Is it the heating controls or the room thermostat which control the valve?

Sorry for all the questions, and help with any of them would be much appreciated.

Massive thanks!

Some photos in case they help:

 

[SJB060685]

If you've not used HW for sometime and CH was the last port of call, which it obviously is, then as you say it's most liked a seized valve or motor, probably the motor because in CH position, whether calling for CH or not the valve is constantly energised and motored over to CH, this burns the motor out, or seizes it.
If you're planning major work in the future then I would suggest repiping and wiring two 2 ports, that way in the future an additional 2 port for UFH will be easy to add.

 

[Ric2013]

The little lever bit doesn't move and stays in auto position. So presumably the valve for one reason or another is stuck and no matter what the controls tell it to do, only port A is open. Does that sound about right?

It's certainly possible. If I remember correctly, the valve will power the boiler so long as it is physically in a position that allows it to close the microswitch.

1. We've got some major plumbing work coming up soon, which will require a full drain down. As such, would it be worth changing the whole unit? I've seen some try just changing the motor, others just the power head. But whilst drained down is it worth spending the extra and just replacing the whole thing?

My feeling is yes, if you're already draining the system and thus not incurring a significantly higher labour charge. A spare head is not a lot less than the whole item and trace leaks on the spindle can (in my experience) lead to shorter lifespans for the new head. It may be worth, in the meantime, removing the head and seeing if the valve spindle can be manually rotated to the DHW position for the summer. If, of course, you have the skill to replace the Synchon brand motor yourself and the spindle seems to free off, this might last another few years. Up to you.

2. My unit is a Honeywell V4073A1088. The one you tend to see most is the V4073A1039. I looked into it and all I could find is the former is 28mm and the latter 22mm. I presumed that related to the pipes feeding it, but does it? The reason I ask is because I have 22mm pipes and yet mine is supposedly the 28mm version. Which has me scratching my head!

Do the pipes increase to 28mm where they enter the valve? I think I see 28-22 reducers on your pipes being used to increase the pipe size where it enters the fitting. Presumably someone had a 28mm valve and 2 reducers were cheaper than a 22mm valve!

3. One forum thread I was reading stated: "“It explains why you can't use a mid position for your HW and RADS and then add a two port for extra rads or UFH.” Is that correct? Is it a blanket statement? Later in the year we are looking to have UFH installed elsewhere in the house, so I'd be interested to know if it would need changing again at some point.

A 3 port is never fully closed, so you can't ever shut it. If you are having UFH fitted, it makes sense to replace the 3 port with two 2 ports, thus allowing the UFH, radiators, and DHW to operate independently.

4. Is it the heating controls or the room thermostat which control the valve?

Heating control usually switches a live feed to the room and cylinder thermostats and the valve rotates according to which live feeds it receives. The valve is entirely electro-mechanical, with no electronics involved.

Sorry for all the questions, and help with any of them would be much appreciated.

Photo of tea and biscuits would be appreciated 😉

 

[Plumb Line]

Photo of tea and biscuits would be appreciated

Well, of course...

A fuller response to follow later 🙂

Cheers

 

[Plumb Line]

Many thanks for the great replies and explanations. I've got to admit, I love learning about this kind of stuff. Not that I always fully understand it though!

If I could bother you with some more questions please...

- Is there no way UFH could be added - as a separate zone - to my current system with 3-port valve? 100% not? Appreciate this is a naive question, but can it be on a completely separate feed from the boiler itself, or does the boiler just have a single flow and single return?

- The reason I ask is because we're not sure if we're going to have any UFH heating yet or not. If we do go for UFH, it would seem a shame to put in a new 3-port unit now only to have to change it all again soon. But if don't end up with UFH, it would be an unnecessary waste and expenditure changing to two-port units.

- Which leads me onto seeing if my existing unit is fixable, in which case we can continue using that until we've decided on UFH or not and then have a new unit(s) installed accordingly. So tomorrow I'll re-read the above, do a little more googling, and watch a couple more vids to see about diagnosing the fault with the unit.

- This is more for my curiosity... I don't mean to be thick, but where exactly does the change from 22mm-28mm take place? I'm pretty sure that when I measured the visible pieces of pipe where they go into the unit they were 22mm. I can take a photo tomorrow. So is the reducer/adapter out of site or am I just not getting something (something which is no doubt extremely obvious to everyone else)?

Right, that's enough excitement for tonight!

Cheers

 

[Ric2013]

- Is there no way UFH could be added - as a separate zone - to my current system with 3-port valve? 100% not? Appreciate this is a naive question, but can it be on a completely separate feed from the boiler itself, or does the boiler just have a single flow and single return?

The boiler usually has a single flow and single return but that's not the question you need to ask. The question is, HOW are you going to run the UFH without also running the DHW or radiators? Think about this and ignore the electrical controls question for now. Your existing valve is always open either to the DHW coil or to the radiator circuit or both: there simply isn't a closed position. If you tee off before the valve for UFH and fit a 2 port on the tee then you can have:
UFH ON with rads and/or DHW ON
UFH OFF with rads and/or DHW ON
but never UFH ON with rads and/or DHW OFF

You could tee off after the 2 port and have:
radiators ON with UFH ON
radiators ON with UFH OFF
but never radiators OFF with UFH ON

- The reason I ask is because we're not sure if we're going to have any UFH heating yet or not. If we do go for UFH, it would seem a shame to put in a new 3-port unit now only to have to change it all again soon. But if don't end up with UFH, it would be an unnecessary waste and expenditure changing to two-port units.

Changing to 2 2 port valves is going to cost more than a like-for-like replacement but should ultimately be more reliable so it wouldn't be a complete waste.

- This is more for my curiosity... I don't mean to be thick, but where exactly does the change from 22mm-28mm take place? I'm pretty sure that when I measured the visible pieces of pipe where they go into the unit they were 22mm. I can take a photo tomorrow. So is the reducer/adapter out of site or am I just not getting something (something which is no doubt extremely obvious to everyone else)?

It's obvious to a trained eye. You have one of these going into your compression nuts on that valve : Endfeed 28 mm X 22 mm Fitting Reducer - https://www.mrcentralheating.co.uk/endfeed-28mm-x-22mm-reducer If it were a 22mm valve, it'd just be a plain bit of pipe going in.

 

[SJB060685]

@Ric2013 that pretty much sums up why I said use three 2 ports.

 

[Plumb Line]

Thanks for the continued great help. I really do appreciate it and understand now. Didn't get the chance to check the unit today but will...

On the subject of UFH, I was just wondering if all boilers are suitable for it? A bit off topic I know, but seeing as I brought up the subject of UFH it got me to thinking. I have a Worcester Danesmoor 20/25 (oil). Can anyone confirm if there's any reason UFH wouldn't be compatible with that boiler?

Cheers

 

[SJB060685]

No reason at all why your boiler can't run UFH as well as long as it's done properly.

 

[Plumb Line]

No reason at all why your boiler can't run UFH as well as long as it's done properly.

Well that's good news then 🙂 Thanks for confirming. Please feel free to nick a biscuit or two off of Ric2013's plate above...

 

[Ric2013]

Well that's good news then 🙂 Thanks for confirming. Please feel free to nick a biscuit or two off of Ric2013's plate above...

Please do. I agree they should be shared!

 

[SJB060685]

Well that's good news then 🙂 Thanks for confirming. Please feel free to nick a biscuit or two off of Ric2013's plate above...

Your old Danesmoor is probably worth considering upgrading at the same time if you're planning on a major overhaul.