Joined
10 May 2017
Messages
34
Reaction score
0
Country
United Kingdom
Greetings all.

I'm after a bit of advice as we have an issue with our HW kettling and on closer inspection the wiring on our 2-port Valves looks a little suspect to my untrained eye.

Background:
The house was built in 2001 and has an 'S' CH/HW System installed. If the HW is on and the CH is not, the HW in the pipes overheats and starts to kettle. We have Drayton ZA6 valves fitted and I know they have an issue where the microswitch can stick and as the original 20 yr old unit was still fitted to the HW side (CH had been replaced at some point) I swapped it out for a new one. I also replaced the Cylinder Stat in case that wasn't switching the pump and boiler off when up to temp.

Now the problem still occurs. The only workaround is to have the CH and HW on at the same time to enable the additional heat to dissipate in the CH circuit.

Wiring Issue:
The cylinder stat does cut power to the valve causing it to close but I've had a closer look at the wiring (still original configuration as the old cables were routed out to make connections to the new cables in a separate junction box). Both HW and CH valves appear to be connected differently to how Drayton instruct.

upload_2021-3-20_11-4-52.png


CH Valve - On our system both the Brown and Grey wires are connected together with the Heating Call for Heat from the Nest Thermostat Heatlink. The drawing above shows that the grey wire should be connected to permanent Live. See Terminal 9 in the photo below.

HW Valve - On our system both the Brown and Grey wires are connected together with the Cylinder Stat. The drawing above again shows that the Grey wire should be connected to permanent Live. See Terminal 6 in the photo below.

From top to bottom the cables are:

Pump
Cylinder Stat
Nest Thermostat Heatlink (N, L, 1 thru 6)
Nest Thermostst Heatlink (T1 and T2)
HW Zone Valve
CH Zone Valve

upload_2021-3-20_11-18-55.png


upload_2021-3-20_11-22-33.png


The way I see it is wiring the valves this way bypasses the microswitch by using the stats to cut power to the boiler and pump. Am I right or have I got this completely wrong? And could this configuration cause the pump and boiler to actually stay on irrespective of valve position?

Many thanks in advance.
 
Sponsored Links

DP

Joined
10 Dec 2003
Messages
15,958
Reaction score
3,682
Location
Glasgow
Country
United Kingdom
The wiring unit standard wiring sequence is L, N, ETH, CH IN, CH OUT, HW IN, HW OUT etc with last two/ three positions for pump and boiler. Apart from remote possibility of back feeding, kettling is not caused by miss wiring the ZV
 
Joined
10 Mar 2007
Messages
10,824
Reaction score
2,332
Location
Poole, Dorset
Country
United Kingdom
That wiring isn't standard, but won't cause the problem described.
With brown and grey connected together, it's impossible for a stuck microswitch to cause the system to run continuously as power is only applied to the switch when the controls are on.
The switched output is still the orange wire, and even with the switch permanently closed, that would only be live with the controls on - unlike a more conventional wiring arrangement where the input to the switch (grey) is permanently live, and if the switch sticks closed, the orange output is also permanently live even with the controls off.

The problem is likely is a restriction to the flow somewhere, either at the valve or in the cylinder itself.
 
Joined
10 May 2017
Messages
34
Reaction score
0
Country
United Kingdom
That wiring isn't standard, but won't cause the problem described.
With brown and grey connected together, it's impossible for a stuck microswitch to cause the system to run continuously as power is only applied to the switch when the controls are on.
The switched output is still the orange wire, and even with the switch permanently closed, that would only be live with the controls on - unlike a more conventional wiring arrangement where the input to the switch (grey) is permanently live, and if the switch sticks closed, the orange output is also permanently live even with the controls off.

The problem is likely is a restriction to the flow somewhere, either at the valve or in the cylinder itself.


Thanks for this. I'm wondering if this is why they've been wired this way because of the issue of these micro switches sticking over time. It's effectively a fail safe as like you say, even if the microswitch is faulty and welded closed, the controls/stat can still cut power to the boiler and pump. Wired conventionally the pump and boiler would still run with the valve closed and the stat triggered open.

Now I've replaced the valve with a new one it might simply be a matter of the boiler and/or cylinder stat being turned up too high for the system. It has a gate valve for a bypass (not ideal) and possibly the bypass circuit is just to short for adequate heat dissipation when the CH is off.
 
Sponsored Links
Joined
20 Mar 2018
Messages
1,640
Reaction score
197
Location
Stoke-on-Trent
Country
United Kingdom
Greetings all.

I'm after a bit of advice as we have an issue with our HW kettling and on closer inspection the wiring on our 2-port Valves looks a little suspect to my untrained eye.

Background:
The house was built in 2001 and has an 'S' CH/HW System installed. If the HW is on and the CH is not, the HW in the pipes overheats and starts to kettle. We have Drayton ZA6 valves fitted and I know they have an issue where the microswitch can stick and as the original 20 yr old unit was still fitted to the HW side (CH had been replaced at some point) I swapped it out for a new one. I also replaced the Cylinder Stat in case that wasn't switching the pump and boiler off when up to temp.

Now the problem still occurs. The only workaround is to have the CH and HW on at the same time to enable the additional heat to dissipate in the CH circuit.

Wiring Issue:
The cylinder stat does cut power to the valve causing it to close but I've had a closer look at the wiring (still original configuration as the old cables were routed out to make connections to the new cables in a separate junction box). Both HW and CH valves appear to be connected differently to how Drayton instruct.

View attachment 227387

CH Valve - On our system both the Brown and Grey wires are connected together with the Heating Call for Heat from the Nest Thermostat Heatlink. The drawing above shows that the grey wire should be connected to permanent Live. See Terminal 9 in the photo below.

HW Valve - On our system both the Brown and Grey wires are connected together with the Cylinder Stat. The drawing above again shows that the Grey wire should be connected to permanent Live. See Terminal 6 in the photo below.

From top to bottom the cables are:

Pump
Cylinder Stat
Nest Thermostat Heatlink (N, L, 1 thru 6)
Nest Thermostst Heatlink (T1 and T2)
HW Zone Valve
CH Zone Valve

View attachment 227389

View attachment 227391

The way I see it is wiring the valves this way bypasses the microswitch by using the stats to cut power to the boiler and pump. Am I right or have I got this completely wrong? And could this configuration cause the pump and boiler to actually stay on irrespective of valve position?

Many thanks in advance.
As others have said, it's not a wiring issue. The system should work without noise with either valve closed. Sounds like reduced flow, due to eg obstruction, or pump problem. Has the problem always been there, or recently started?
 
Joined
10 May 2017
Messages
34
Reaction score
0
Country
United Kingdom
As others have said, it's not a wiring issue. The system should work without noise with either valve closed. Sounds like reduced flow, due to eg obstruction, or pump problem. Has the problem always been there, or recently started?
It's been there since we moved in 4 years ago. I may have noticed it only once we had the Nest installed and I turned up the stats and reprogrammed the timings. The work around has been a mixture of turning the cylinder and boiler stats down or programming the water to come on only when the heating is on. I also opened the bypass a little more but in truth that circuit gets extremely hot. This is probably what the previous owner did. I've just turned the cylinder stat down from 60 deg c to 55 deg c.

The pump is on the mid setting.
 
Last edited:
Joined
20 Mar 2018
Messages
1,640
Reaction score
197
Location
Stoke-on-Trent
Country
United Kingdom
It's been there since we moved in 4 years ago. I may have noticed it only once we had the Nest installed and I turned up the stats and reprogrammed the timings. The work around has been a mixture of turning the cylinder and boiler stats down or programming the water to come on only when the heating is on. I also opened the bypass a little more but in truth that circuit gets extremely hot. This is probably what the previous owner did. I've just turned the cylinder stat down from 60 deg c to 55 deg c.

The pump is on the mid setting.
Might be worth checking the pump. I had a problem of slight kettling, not really bad enough to worry about, but at one point the pump started to vibrate badly. I replaced it and the the noise disappeared. When I dismantled the old pump the impeller (two stainless steel discs with a gap of about 2mm) was completely clogged. So improving the flow made all the difference.
You should be able to remove the motor and impeller without disturbing the pipework.
 
Joined
10 May 2017
Messages
34
Reaction score
0
Country
United Kingdom
Might be worth checking the pump. I had a problem of slight kettling, not really bad enough to worry about, but at one point the pump started to vibrate badly. I replaced it and the the noise disappeared. When I dismantled the old pump the impeller (two stainless steel discs with a gap of about 2mm) was completely clogged. So improving the flow made all the difference.
You should be able to remove the motor and impeller without disturbing the pipework.


The thing is the pump is perfectly quiet with no vibration. The water is the pipes gets so hot it's effectively boiling up before banging and eventually dissipating. I reckon it's turning into steam. This only happens with WH on and CH off so if it's not electrical it's got to be insufficient flow in the bypass circuit. I can get it to do it easily enough with a tank full of hot water. Turn on HW Boost with CH off, wait a few minutes and the settling starts. Pipe work far to hot to touch. I did this earlier and when it started to kettle I backed off the Cylinder stat which closed the valve. I then confirmed the boiler was also now off.
 
Last edited:

DP

Joined
10 Dec 2003
Messages
15,958
Reaction score
3,682
Location
Glasgow
Country
United Kingdom
With brown and grey connected together, it's impossible for a stuck microswitch to cause the system to run continuously as power is only applied to the switch when the controls are on.

Assume CH and HW is on, Both aux switches in the ZV are made. CH time comes to an end and relay in the programmer removes the 240 off the CH on tag. 240 that is running the boiler (via HW ZV) will back feed through CH zone valve aux sw to keep the CH valve open till room thermostat is satisfied.
 
Joined
10 May 2017
Messages
34
Reaction score
0
Country
United Kingdom
Assume CH and HW is on, Both aux switches in the ZV are made. CH time comes to an end and relay in the programmer removes the 240 off the CH on tag. 240 that is running the boiler (via HW ZV) will back feed through CH zone valve aux sw to keep the CH valve open till room thermostat is satisfied.

Back through Orange > Grey and across to Brown? If temp not satisfied, power to valve, valve opens, microswitch is closed, grey to orange and boiler and pump run?
 
Joined
20 Mar 2018
Messages
1,640
Reaction score
197
Location
Stoke-on-Trent
Country
United Kingdom
The thing is the pump is perfectly quiet with no vibration.
So was mine until the vibration started, but I still had the kettling because of low flow (it turned out). When I took it apart there was a stainless steel ring pressed into the pump casing which had come adrift.
 

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
Top