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Put your Central Heating System question in here.
By Miket201
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.
By Miket201
(We may have two pumps due to there being underfloor water heating in a couple of rooms downstairs and needed extra power to get heat all around the house).

I've not been able to get the hot water cylinder inlet pipe hot, just warm and just warm coming through the showers.

The heating and HW has been on for the last couple of hours now and although yesterday the top inlet pipe going into the hot water cylinder in airing cupboard was hot,
today it just seems a little warm, as does the bottom one.

I've turned off HW and heating and I can slide the HW ZA5 open and it then closes, then when I turn the HW on the slider locks into the open position and cannot be moved.

I have turned the HW off and locked the HW ZA5 to the open position and turned the HW on but still there is no HOT going beyond the ZA5 to the cylinder. The ZA5 is locked into the open position.

Would it do any good to try swapping both (hot water and heating) ZA5 actuators (the heads) and seeing if the heating then has any problems instead ?

Can it be swapped without any problem as maybe they are wired in the same ?

I'm assuming when I click them off and on again it's with the slider in the closed position ?
Can they be put on incorrectly ?

Sorry for so many questions.

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By Best
The hot water zone valve might be critical part of the cylinder if it is an unvented cylinder, so got to be careful not to cause it to keep heat passing.
The head could be faulty and swapping might confirm that. They often intermittently fail.
Best a G3 unvented qualified plumber takes a look at it and serviced the lot if unvented cylinder.
User avatar
Miket201 wrote:
January 27th, 2020, 4:02 pm
Hi, I've chatted to Drayton and they confirm after trying various options that it's the ZA5 zone valve that is faulty, so I'm going to change the actuator head once I turned all the electrics off.

just taking the head off the valve whilst the systems running can normally test it as the water will push open valve.

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