Hot Water Tank, Thermostat Not Working

Berty

Hello,

Where do I start with this issue(no suggestions of getting in a plumber(or similar) yet please?

The house was built in 2007 so a relatively modern hot water tank in the hotpress. Irrespective of what temperature I select the dial to it seems to be heating the water to FULL HEAT.

Where do I begin with getting it back to normal?

Thanks in advance.

Pete67

Can you post a picture of the hot press? Is it an electric immersion heater, or oil/gas central heating that is heating the hot water cylinder? If you are using an immersion the thermostat is not visible, it is built in to the top of the immersion heating element and you need to remove the cover to adjust it (beware live terminals inside).

If there is a thermostat attached to the lower half of the cylinder, this is probably associated with a motorised valve to shut off the heating coil in the cylinder. If the valve has failed in the open position, or the manual over-ride is holding it fully open, then the thermostat will have no effect. Depending on how the wiring is set up this could also cause the boiler to run continuously. The thermostat itself could also be faulty.

Berty

Gas Heated.

3 Siemens Boxes all set in the Auto Position and have been always.

Thermostat set to Lowest Setting 20c



3 Siemens Boxes all Set to Auto



And the Top

TPM

The cylinder stat in the photo will only control the temperature of the water from the gas heating, the immersion will still heat the cylinder fully regardless of the position of the cylinder stat.

With the gas heating turned on if you turn the cylinder stat up and down, one of the motorised valves(siemens) probably the vertical one should open and close, does this happen

Berty

TPM wrote: »

The cylinder stat in the photo will only control the temperature of the water from the gas heating, the immersion will still heat the cylinder fully regardless of the position of the cylinder stat.

With the gas heating turned on if you turn the cylinder stat up and down, one of the motorised valves(siemens) probably the vertical one should open and close, does this happen

Yes I can hear a click from one of the valves. We do not use the Immersion switches so it's not the issue with that function of it. The water is scalding to the touch.

Pete67

Sounds like the Siemens valve is faulty. Is there an indicator light on it and does it light up when you turn the thermostat to max and go out when you turn it back to minimum - if so, and the valve does not move then the actuator on the valve is faulty. You might be able to replace just the actuator without draining down and removing the valve itself.

Berty

Assuming it's the DVA2/5 Demountable Valve, is it just a quick/cheap fix to replace this myself rather than calling out a heating Engineer?

Online about €25-35

Replace just the Mounted Section rather than the joint first or replace both straight away? (some places sell just the siemens section and others both(22mm) in a box)

I should point that that if I turn the Thermostat on the Tank from one extreme to the other it doesn't always click which is odd because I would have imagined it would open and close on the up and down movement of the temperature setting but it doesn't.

Pete67

If the cylinder thermostat is not working properly it could also cause the problem. It is unlikely that the 22mm valve is faulty, but it is easy to test - just remove the actuator and see if the valve spindle turns freely.

If the actuator does not turn when you adjust the thermostat from one extreme to the other then to find out which is at fault you need some electrical knowledge and a multimeter. It's not difficult but to do it safely you need to know what you are doing - all wiring is at mains (230V) voltage and could easily be fatal.

Berty

Another question.

I have come to the conclusion that the DVA2/5 feeding into the boiler is not working. I had removed it and found that it has something wrong with the movement of the spring. It is also hot to the touch so clearly needs replacing which I will do Monday when I can get one.

Now, I have left the valve open, with the actuator removed, and the heating only comes on for about 1.5hrs twice a day(by choice). However, the system is not reacting with the thermostats upstairs/downstairs. Even though the light goes off on the units, suggesting the temp I set has been reached, the heating still continues and heats the house to FULL temperature.

Is this because the 3 actuators are linked and the fact I have the valve open(turned it open with flat head screwdriver) causing the problem?

Iderown

Here's what is probably the most popular arrangement of the switching electrics for a three-zone (upstairs, downstairs, hot water cylinder) system.

1. The relevant thermostat activates the relevant motorised valve.

2. There is a microswitch in each motorised valve. They are connected in parallel with each other. This performs the logical OR function. Mains live is fed to the burner when any one, or more than one, of the thermostats are demanding heat.

3. A thermostat sensing the water temperature in the boiler, interrupts the demand feed when the boiler water temperature is at maybe about 70C. An additional one stops the boiler working if the temperature should go above 95. This is the pop-out re-settable one.

4. A further permanent live feed to the boiler controls the circulation pump via yet another thermostat sensing the boiler water temperature. It switches the pump on when the boiler water temperature reaches maybe 40C. (The activation arrangement for the circulating pump may be different.)

A problem that we had with the HWC thermostat was that it was positioned so low on the cylinder that it could never be affected by the hot water circulating in the coil within the cylinder.

Hope this helps

Berty

Heating Eng had a look at it. Wants to replace all 3 valves with Mysons + Labour.

Only one valve in my opinion is shot but he says it's best to replace all 3 together which is a fair assumption.

Fair enough €220 total which is fair enough because the labour is only €40 although I have a replacement Siemens Actuator coming tomorrow so will try that first.(It essentially cost me nothing with some wheeling and dealing) so if all fails €220 will be shelled out.