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

wrote:
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.

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.

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

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

In an earlier contribution to this discussion,
wrote:

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

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

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.
--
Cheers,
Set Square
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