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I have a Glow Worm 24HX Condensing boiler on the ground floor with a pump in the same cupboard, a hot water storage cylinder in the airing cupboard upstairs (Kingspan 1500 x 450 grade 3, 162 Litre. cylinder) in the eaves area I have another pump (both pumps are Salus MP200 domestic circulating pump). Upstairs I have two Drayton 2 port Zone Valves ZA5, one on the hot water supply to the hot water cylinder and one to the central heating supply.

The hot water and central heating is timed to go on in the afternoon 4pm to 1030pm every day and has been working fine for the last 7 years, I think the whole system is around 11 years old.

One evening I found that the temperature of the water coming out of the upstairs shower was warm and I couldn't get it to go hot, no matter how much I adjusted the shower control

I then checked the temperature of the pipe coming out of each ZA5 valve, heating pipework was hot entering the valve and leaving the valve.
Hot water pipe was hot going into the ZA5 valve but only a little warm going out, towards the hot water cylinder.

I turned off heating and hot water via the timer and could move the slider switch on both ZA5 valves and they would then return fine by themselves.
I snapped off the electric head of each and couldn't see anything (although I understand I probably wouldn't see anything unless they were dismantled) and
snapped them back on.

Now I seem to find that there is hot water in the evening. I'm assuming that having moved the sliders on each ZA5 valve has maybe freed the hot water ZA5, sticking maybe? but now there does not seem to be any hot water in the morning, whereas their used to be hot water all day long (left over from the night time).

I'm just wondering if I changed the snap on ZA5 zone valve (actuators) would help and is it worth changing the whole valve including the compression pipework ?
I have not changed any hot water temp on the hot water cylinder thermostat.

Is it ok to just change the snap on ZA5 actuator part on the zone valves (£52) and not having to drain the system,
or for the sake of £12 extra is it better to change the complete value with pipework attached but would mean I have to drain the system down first ?

Any help or suggestions as to trying to diagnose what is causing the problem and ZA5 actuator or whole unit replacement would be much appreciated.
There is an A and B labelled slide of some kind on the side of the ZA5 that does not seem to move, not sure if that is important.

I'm going to keep running the heating / hot water as normal over the few days to see exactly what is happening.
Apologies for the length of this post.

Many thanks.
Mike
 

Murdoch

Res.Electrician
What happens if you run the water only?

Does the thermostat on the water tank operate properly?
 
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What happens if you run the water only?

Does the thermostat on the water tank operate properly?
Hi, I'm away this weekend but I will try Monday morning, thanks.
Post automatically merged:

Hi, I'm away this weekend but I will try Monday morning, thanks.
Hi, someone suggested turn off CH and HW, lock the ZA5 HW zone valve to open then turn on the CH. I tried this and everything started to cool down and the boiler turned off. A little later I turned CH and HW on and everything works fine. I also tried just HW and that seems fine also. The spindle on the valve seems to turn fine by hand so not stuck, and the valve seems to be working fine, maybe it's temperamental.

What is this one supposed to do? If it circulates heating water from the boiler though the cylinder coil it's a possible suspect.
(Re cylinder coil). I don't really understand this answer but many thanks for your suggestion.

I will probably wait for the problem to re occur then look to change the ZA5 actuator head.

The thermostat on the hot water storage cylinder seems to work fine also.

Many thanks for all your suggestions.
 
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