Help Troubleshooting Heating Issue

[Zeltrax]

Hi everyone,

I'm really struggling to diagnose the issue with my heating, and I could use some advice.

About a week ago, my central heating suddenly stopped working, but my hot water has been fine. I’ve replaced my Nest 3rd Gen thermostat and redone all the wiring, but the boiler still refuses to stay on.

Here’s what’s happening:

• When I set the temperature, the 2-way valve opens, and the system runs for about 10 minutes.
• After that, the valve closes, but the thermostat still shows that the target temperature hasn’t been reached.

As a temporary workaround, I’ve set the thermostat to 0, manually opened the 2-way valve, and removed the tank thermostat. This gives me minimal heat, but it’s not ideal.

With my wife being pregnant and upgrading the boiler not an option until summer, I really need to make do with what I have. Any suggestions on what could be causing this or how to fix it?

My boiler system is an S plan and its a normal boiler IDEAL Icos HE18.

No errors on boiler or on the google nest.

Boiler and Nest have been working for 2 years no problem also tested the central heating external pump and that is fine.

Thanks in advance!

 

[terryplumb]

Before you did the " temporary workaround" ,you told us boiler fired up for ten minutes for central heating ( with no demand for domestic hot water I assume ) and the zone valve then closed. How did you establish the zone valve closed / what did you do to determine that ?

 

[Zeltrax]

The next day, I noticed I had no heating. I turned the thermostat up to 24°C and went to the boiler to observe its operation. I watched as the boiler fired up and the central heating zone valve opened. I listened carefully for any unusual sounds.

After about ten minutes, the zone valve closed. A minute later, the boiler became quieter, and a few minutes after that, it turned off completely. However, when I checked the thermostat, it was still showing that it was trying to reach 24°C from 16°C.

These times varied over the week after trying to troubleshoot the wiring, then RMA'd my thermostat because I thought the heatlink was the cause.

 

[terryplumb]

How did you establish the zone valve closed / what did you do to determine that ?

Specifically please.
Do you have any voltage testing instruments?

 

[Zeltrax]

Specifically please.
Do you have any voltage testing instruments?

Its a honeywell motorised port zone valve it was a visual inspection of seeing it close by itself. Haven't taken a multi meter to it yet but I used an electric pen which showed power running through the cable.

 

[terryplumb]

There is voltage permanently going to the zone valve, as long as the system is energised, which goes to the valves internal micro switch. When the thermostat/ programmer etc calls for heat further voltage is supplied to the zone valves motor which causes the motor to open the gate in the pipework allowing water to pass through ,and when the motor reaches the end of its travel it operates the micro switch . The permanent voltage at the switch is then connected to the boiler to fire it up.
Checking voltages at the wiring centre should indicate why the zone valve closes.

 

[CountryFan]

I used an electric pen which showed power running through the cable.

That will show the permanent live as per @terryplumb. It does not give you an indication that voltage is present, nor if there were, how much.