Programmer will not display CH without HW

28 Jan 2019
Reaction score
United Kingdom

First post :)
I have Y plan system for CH and HW via 3 port valve, Honeywell 4073, pump on its input side.

The CH works whilst HW is on at programmer (Potterton EP2000), but CH does display or work when HW is off at programmer, even if room stat is calling for more heat.
It has been the same since I moved in 4 years ago and previously assumed that was the way it had been set up, but time now to resolve .

In checking for a fault I note if I turn manually HW to OFF on programmer (via slider switch), the CH on the electronic display also goes off, even though slider is set for "24 hours" which seems odd.

I have read that a faulty 3 port valve (micro switch) can mean the CH does not run independantly, so the 3 port valve is perhaps to be suspected.
Q1) Would a 3 port valve (switch) probelm also explain the programmer not allowing CH to be displayed ON, on it's own?
If 3 port valve is faulty, my laymans expectation is that programmer will still display CH, as that is what it is supposed to be trying to set itelf to.
Many web articles talk of the no CH without HW problem, not don't mention whether this prevents programmer from displaying what it is TRYING to achieve.. even if microswitch faulty.
The genuine Honeywell replacement head is expensive, so would like to check the theory first.

Q2) Is there any other reason why the programmer would turn off the CH on its display when it turns HW off?
I have checked it is in the 16 programme position for pumped systems and that the HW off wire is present at the programmer.

Sponsored Links
Update. Spoke to a heating engineer over the phone.
It seems I am perhaps assuming the programmer is more intelligent than it is and if programmer won't display CH with HW off, then either it is in the 10 program gravity mode not 16 program pumped mode, or it is a problem with the programmer.
I had checked it was in 16 mode already, so seemingly a programmer fault.
I have ordered a Potterton EP2 the modern equivalent of the EP2000, should have the same backplate, so I can swap without any wiring.
It was £72.
I was reluctant to replace the old one as I plan to instal a smart version, but I want to ensure any current problems are resolved or identifiable, before I instal new kit.

After further investigation I believe I have a problem with 3 port valve on the Y plan.
If programmer is set for HW + CH, that works fine, I have HW and CH.
If room stat is turned down, radiators cool, as expected. (Does this alone mean 3 port valve motor is working?)
If room stat turned up, radiators warm again. Good, as expected.
If cyl stat is turned down to a low setting, the HW side of the valve still feels hot.
As far as I can tell, the valve never goes into the HW fully closed position.

I believe the 4073 valves changed in 1985 to having 2 screws to replace head, rather than 4.
I have the old 4 screw type, so cannot remove the head to test without draining.
I could change the motor, but as it change from HW+CH to HW only, I assume the motor is working.
I cannot hear any crunching of gears.
What could be wrong with the valve?

I have found old (pre 1985) Y plan wiring diagrams for pumped systems, showed "CH cannot be selected without HW".
It seems odd, but can only assume this was a feature built into programmers at the time and so a red herring to my fault diagnosis in my first post above.

On a Y plan, you can have HW by itself, CH by itself or both CH and HW

Old type valve or one with removable head, makes no difference if valve is 4073
You are looking for defect that might not be there, just wiring error
Sponsored Links
Thank-you DP.
I have checked the wiring is as per Y diagrams and all corrrect.
Awake in the night trying to make sense as it is non-sensical.
If motor will turn CH off it must be working, so at a loss why it won't move into CH only position.
I have read gearbox can go but don't hear any noises to suggest this.
IIRC I read that one of the 2 valve microswitches is to turn the boiler on when needed(so seemingly not the issue here), but I don't know what the other one does.
post a pic of the wiring and backplate of your programmer, you need a wire in the HW off terminal which should be linked to the CYL stat satisfied which then tells the mid position valve to close the DHW port
Thank-you Ian. I can confirm there is a HW OFF cable from Programmer to TB7 then green to cyl stat and grey to valve.
I have pics, not sure if it will help as been same since house built around 1982.
All as per standard Y plan except pump is not via boiler over-run (checked with Boiler m/f that boiler does not have overrun).

I'd recommend buying a cheap multimeter, something like this

Set it to the highest AC Voltage range (600V~ in this case) and check that the HW OFF (240V) is actually present when it should be.

Then you'll have a better idea if the problem is down to the programmer itself (ie a fault or incorrectly set up for a fully pumped system), or something else.
Last edited:
Thank-you Jackthom.
I have a multimeter and a printed off the web the expected voltages for each position.
I was hanging back from testing with multimeter in case I accidentally shorted something, as don't want to be without heat whilst freezing outside.
Multimeter has setting for 200 and 600 AC, so I'll go with 600 as you suggest.
..just back from shopping.
Before leaving I turned the cyl stat down from around 65 to around 45.
The radiators are getting hotter than they have been before!!!
This is news!
It would suggest the HW port is closing - at least part way, though I can't put my hand on either the HW pipe going into cyl or HW exiting cyl as too hot, even though port supposedly closed.

In my testing I could hear the cyl stat clicking, so seems to be working.
So.. if rads are now hotter, that would suggest there is no problem.

In normal use, HW and CH both set to ON, cyl stat is at 65, even if I don't use HW, the rads only get warm.
I know the above sounds contradictory.

Maybe 65 is too high for cyl stat and never satisfied or maybe there is gunge blocking HW port, so never completely closed.
Or the rubber ball thingy is falling apart, so not fully closing either port.

More head scratching. :)
you may need to fit a restricting valve on the return from the secondary coil in your HW cylinder, the flow of hot water from the boiler will always take the easiest route , so will go through the coil rather than a radiator, it is common practice to install a gate valve and partially close it to force the water through the rads
There is a valve there, top looks like a bleed point for air.
I am familiar with concept, but don't know how to adjust them and what I am aiming for.
I have a shower that can use HW at high rate, so wouldn't want to compromise that.

You have hit on something good there!!!
Any tips on how to set appreciated, but I can google that dinner ready now, so I'll do that next.

I have found youtube videos on pressure relief valves but nothing for restrictive valve, apart from passing reference in one video, that said they should be on the output side.
Mine is on the input side, which I would have expected to be right - if it makes any difference at all.
I could get rad key into top of above valve, but found the top collar is only thumb tight and comes off to give spanner access, so gave 90 degree turn to close slightly, to suck it and see.

Is there a standard term for them, "restrictive valve", "balancing valve", the latter only gives me rad balancing.
A side question please. :)
In checking the wiring some cables are buried in the wall and I can't see the back of my boiler (installed circa 1982).
As far as I can tell, there is only one power cable to it, a switched live, whereas most Y plan diagrams show a switched live and a permanent live.
Do some boilers function without a permamnent live?

Once above problem is fixed I plan to instal a smart thermostat and HW programmer. Nest is looking favourite at the moment.
It will be an opportunity to instal a prettier wiring block. :)
yes some boilers need a permanent live sone just use a switched live, the valve I described is just a simple way of reducing the flow through the coil in your HW cylinder, a cheap gate valve will suffice
Thank-you Ian.
I have spent many hours checking the wiring, watching youtube videos and will test over the next few days, but your give away one liner has largely answered the question!!!!
It would seem though it is only a part of the problem. I am guessing the ball inside maybe partly perished. Would you agree?
Is it worth draining down and replacing it or is it normal for the valves to let some flow go by when supposedly closed?

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links