Suddenly in Hot Water!

[marcus]

Hello,

Can anyone think if a reason as to why the hot water coming from my hot water tank has suddenly got very hot? Even though I have turned the thermostat right down the water is scalding hot. In fact, adjusting the thermostat does not seem to have any effect at the moment.

I've not done any plumbing jobs or done anything to the hot water tank other than having to take the lid off the cold water cistern on the weekend to replace a washer in the ball valve. In the process I did have to disturb the expansion feed from the hot water cylinder that feeds into the top of the cold water cistern. Could this be the cause of the sudden increase in my hot water temperature?

If not, does anyone have any other suggestions as to why this might be suddenly happeing and any suggestions as to how to rectify it?

Thanks in advance.

Marcus

[marcus]

Hello,

Can anyone think if a reason as to why the hot water coming from my hot water tank has suddenly got very hot? Even though I have turned the thermostat right down the water is scalding hot. In fact, adjusting the thermostat does not seem to have any effect at the moment.

I've not done any plumbing jobs or done anything to the hot water tank other than having to take the lid off the cold water cistern on the weekend to replace a washer in the ball valve. In the process I did have to disturb the expansion feed from the hot water cylinder that feeds into the top of the cold water cistern. Could this be the cause of the sudden increase in my hot water temperature?

If not, does anyone have any other suggestions as to why this might be suddenly happeing and any suggestions as to how to rectify it?

Thanks in advance.

Marcus

[Dave]

Check the tank thermostat and the 3-way (or zone) valve.

Dave

[Aidan]

Is there a boiler involved ( indirectly heated hot water storage cylinder) and/or is there an electric immersion heater.

The contacts on electric immersion heaters can weld themselves together, so that they fail in an On/unsafe condition. If you have an immersion heater in the tank, I'd suggest you turn it off.

This will either;

a) stop the water heating altogether (new immersion heater thermostat required) or b) will have no effect (the problem was in the boiler controls).

In either case, it will render the main hazard safe. Do that & report back for further suggestions if needed.

[marcus]

Hi,

It is an indirectly heated hot water storage cylinder. It has a thermostat. It also has an imersion heater but this is currently turned off and the immersion heater has not been turned on at all recently.

Could the cylinder thermostat have failed or are there other boiler issues or potential control problems that this could be related to? As I noted in my original post, I have turned down the cylinder theremostat but it seems to have no effect.

There is a box at what I would call a T-junction which I think is the control valve. The pipes on both sides of the "T" are warm to the touch if this helps. Does that mean that the value is working properly and does that narrow things down to the cylinder themostat?

As I also noted in my original post I noticed the problem after fixing a ball valve in the cold water cistern. To do this I had to remove the lid of the tank which involved slightly "shifting" the vent pipe from the hot water cylinder. It isn't possible that this caused the problem is it? Or is it just a coincidence that I noticed the problem after fixing the other problem with the leaking ball cosk.

Thanks again for any help.

Marcus

[Set Square]

From your description, you have a Y-Plan system with a 3-port mid-position motorised valve. This is supposed to direct water from the boiler either to the indirect coil in the hot water cylinder to heat the hot water, or to the radiators - or both together.

When the hot water demand is satisfied, but space heating is required, the valve should be in the CH-only position. I would put my money on it being in the mid-position instead - so that whenever the central heating is on, the hot water continues to get heated - well above the tank stat setting (with the tank stat having no effect).

This is due either to the partial failure of the actuator (the electrical bit on top of the valve) or to the wet part of the valve being jammed. To find out which, you need to remove the 2 screws holding the actuator onto the valve, and then take it off. To check whether the valve itself is jammed, see whether you can turn the spindle by hand (or with light pressure using a pair of pliers) through 45 degrees either side of the centre position. If jammed, you will have to replace it - which involves partially draining the system.

If the valve is ok, adjust the programmer and tank thermostats to call for:

• hot water only

• heating only

*both together and see what the actuator does (while connected electrically but removed from the valve).

You should see it take up each of its 3 positions - but I suspect that it won't get past the mid position - in which case you'll need to replace it.