Boiler not turning off - Honeywell V4073A valve problem

[Tykey]

Hi all,

I'm looking for a bit of help. I have an issue where my boiler is not turning off even when the programmer has CH and HW set to off. Alongside this, if I have HW on, then some of the radiators upstairs start to heat up. This leads me to believe that the Honeywell 3 port motorised valve is the issue.

The question I have is, how can I narrow down the part that's the problem? I understand it's possible to replace just the synchron motor, the whole head, or the entire valve (in that order of ascending expense and simplicity).

I've had the metal case off the valve (it has a dimple!) and when I slide the lever from manual to auto, there is no resistance and none of the springs move.

Is anyone able to shed any light on what bit I need to be looking at changing? Many thanks in advance.

 

[ianmcd]

the dimple means that you can change the actuator but sounds like the synchron motor has seized, make sure you isolate the power before attempting to change.

 

[Tykey]

Thanks. That will be my first point of call then, and then if that doesn't work, I guess I'll move up the chain and replace the actuator. Looks like the motor is about a £12 replacement, so fingers crossed that's what it needs.

 

[ianmcd]

you will know if it is the actuator as soon as you remove the retaining screws , if the actuator has seized the valve will spring into the proper position

 

[Tykey]

Replaced the motor this afternoon, and no dice.

Any idea if there's a way to be sure that replacing the whole head will solve the problem? As in rule out the valve itself as the problem?

Just don't want to do that and then find I need a new valve anyway so could've just bought the whole thing.

 

[hertsboilers]

Take the valve head off the base (if it is detachable by two screws, not by four screws!), check the spindle rotation, lubricate it if necessary.

 

[Tykey]

Thanks. It's definitely got two retaining screws, so presumably that means I won't be getting wet!

I'll take it apart in the morning and see if I can rotate it manually and go from there. Cheers.

 

[Terrywookfit]

The spindle does not rotate.
It only has a small arc of movement !!

 

[Tykey]

Indeed, wrong choice of word. I will turn it slightly, not rotate it fully!

 

[Tykey]

Ok, so I removed the head from the unit, and the spindle is pretty stiff. Applied some lubricant, but it can still only be turned using pliers and not by hand.

Also, I fitted a new head to test it (no power connected yet) and when I take it off the manual position it doesn't spring back to auto which I presume it should.

I know on a brand new valve it's very easy to turn by hand, so my presumption is that the valve is the issue, that's probably what killed the head unit, and the whole part will need replacing.

Next question, this will require me to drain down the system. Is this something that I, a moderate DIYer can do with some advice from you helpful chaps, or is it time to call someone in?

 

[Jajodu]

You can change just the ball assy on the valve. Drain the system to below the valve, undo a coupkr of screws and the valve can be removed. New ones come with a new O ring.

 

[Tykey]

Thanks. I have a new ball assembly that I will change over, but just need to drain down the system first.

Next question, I thought so had a gravity-fed system (i.e. I have a tank in the loft) but I also have a pressure valve at the top of the hot water cylinder, with a braided pipe and a valve to add water to the system. I thought this was indicative of a pressurised system, but I have no sign of a pressure vessel anywhere. Is this normal?

It's a relatively new house so I'm still trying to get to grips with what pipework leads to where.

 

[terryplumb]

Pics of hot water cylinder and associated pipework may help

 

[Tykey]

Thanks Terry, I've tried to show as much as possible.

This is the offending Honeywell valve that needs to be replaced.

View media item 100871
View media item 100872
This is the top of the tank, where you can see the pressure valve, braided pipe and black valve to open it to add water.

View media item 100873
View media item 100874
These five pipes head up into the loft

View media item 100875
This is where they come into the loft. One (hot) goes straight to the pumped shower controller box, two cold come out of the side of the loft tank at the bottom, one goes to the ball-cock in the tank (mains) and one is the expansion pipe that goes up and over.

View media item 100878
These are the two that come out of the side of the tank, and the third along the bottom is the mains to the tak.

View media item 100876
This is where the mains goes into the tank, and a third outlet at the bottom that is the cold feed for the pumped shower.

View media item 100877
Hope that all makes sense. So to me, this looks like a gravity F&E system, but I'm just confused to see the pressure valve at the top of the cylinder. Any advice would be appreciated.

 

[terryplumb]

Tank in loft feeds hot water cylinder ,and shower pump. So your domestic hot water is gravity fed. It looks like your central heating circuit ( which also runs through a coil inside the hot water cylinder ) is sealed / pressurised. There has to be an expansion vessel somewhere .what is your boiler ,make model etc.