I have a townhouse, an unvented hot water system and a combi boiler. My
cols taps on the top floor run HOT for around 5 minutes. I have also
noticed that the water in the tiolet is also hot to the point that if
you sit on the toilet you can burn your back.

Anyone have any ideas? Is this issue a health problem.

Plus as my hot water is on 24/7 this could cost me in more ways than
one any ideas on how I could calculate the cost?

Cheers

Kris

I have a townhouse, an unvented hot water system and a combi boiler. My
cols taps on the top floor run HOT for around 5 minutes.

I'm not sure if you mean you have an unvented cylinder, or just a combi
boiler. If it is an unvented cylinder, turn it off immediately. Ensure that
the immersion is off and the heating coil isolated. Then get a specialist
plumber qualified on unvented systems to look at it. When unvented cylinders
go wrong, they can explode with dire conseqences (i.e. total destruction of
the house). This doesn't sound like one of the dangerous failure modes, but
it pays to be careful.

If it is a combi, I suspect that you either have misplumbed hot and cold
water, or more likely, a shower valve without check valves that is passing
water between the hot and cold systems. The same problems would also affect
an unvented cylinder system, but combis are fundamentally safer and less
likely to explode.

Christian.

Thanks for the quick response.

The unvented part I refer to is the hot water system, it is basically a
big water tank on the top floor. The boiler heats this and also
provides the heating.

I have had strange noises cumming from the water tank but presumed that
this was just normal.

Also the cold water runs cold after around 6 mins and the hot stays hot
so I dont think it could be plumbed wrong.

Is the chance of explosion that bad? I have three young children on
that floor!

Kris

Is the chance of explosion that bad? I have three young children on
that floor!

Oh yes. It is very bad. On the plus side, it seems to me that the failure
mode you are seeing is unlikely to be one of the ones leading to explodion.
However, there is no guarantee of this and you should get a specialist in
very quickly.

I still think that the most likely cause is a malfunctioning mixer valve,
probably a shower.

Christian.

wrote:
Thanks for the quick response.

The unvented part I refer to is the hot water system, it is basically a
big water tank on the top floor. The boiler heats this and also
provides the heating.

I have had strange noises cumming from the water tank but presumed that
this was just normal.

Also the cold water runs cold after around 6 mins and the hot stays hot
so I dont think it could be plumbed wrong.

Is the chance of explosion that bad? I have three young children on
that floor!

Not if its plumbed correctly..there are mandtory relief valves and
overflow lines. However if its boiling it could be an issue. Faulty
thermostats can do that.

Kris

wrote in message
oups.com...
I have a townhouse, an unvented hot water system and a combi boiler. My
cols taps on the top floor run HOT for around 5 minutes. I have also
noticed that the water in the tiolet is also hot to the point that if
you sit on the toilet you can burn your back.

Anyone have any ideas? Is this issue a health problem.

Plus as my hot water is on 24/7 this could cost me in more ways than
one any ideas on how I could calculate the cost?

Cheers

Kris



Yes, I agree that you need proffesional help.
In the meantime, here's a couple of things to try:

I've seen this on an un-vented system where the one-way expansion checkvalve
on the cold inlet had stuck open, allowing hot water to expand back to the
balaced cold tee-off. It couldn't expand further back upstream into the
mains, due to another checkvalve in the 3-bar pressure reducing valve.

Identify the valves as follows:

Follow the cold feed back from the cylinder inlet. It will come to a valve
with a knob on it. This is the Expansion checkvalve / expansion relief
valve.

It discharges into a plastic cone thing called a tundish.
It is essentially a visible overflow.

Observe the tundish for flow. Is their either continuous or intermittent
flow in the tundish? That indicates a problem.

Check that the expansion relief valve is not stuck shut by twisting the knob
and checking for a discharge of water in the tundish. Carefull! it will be
hot!

Feeding into the tundish will be a second valve with a knob on it, directly
on the cylinder. This is the Temperature / Pressure relief valve. Give
it a quick twist and ensure it discharges too.

If both of these discharge on twisting, and neither is discharging unless
you twist them, then the thing is most likely safe at least. So you have
some peace of mind untill a qualified person can check it.

Feel the cold inlet pipes at the unvented cylinder. It will be hot at the
point where it enters the cylinder. If it get hot upstream of the expansion
check valve, then there's a problem there.

Another possible problem is the possibilty that the air volume in the
expansion unit has become depleted, the usual symptom of this is
intermittent discharge from the expansion relief valve. This is not a big
problem to fix if it's happening. In any case, it should not expand back
through the expansion check-valve, however.

A possibility that no-one has mentioned is bad pipe routing.
Does the cold pipe run hard up alongside a hot pipe anywhere, allowing a
pipe-volume to heat up?
That would normally run off in a few seconds, not a few minutes.

If it's taking a few minutes, then it sounds like an expansion volume, and
that as I say points to a problem with the expansion check valve. Probably
not a safety issue, but in need of qualified attention.

--
Ron

wrote:
I have a townhouse, an unvented hot water system and a combi boiler. My
cols taps on the top floor run HOT for around 5 minutes. I have also
noticed that the water in the tiolet is also hot to the point that if
you sit on the toilet you can burn your back.

Anyone have any ideas? Is this issue a health problem.

Plus as my hot water is on 24/7 this could cost me in more ways than
one any ideas on how I could calculate the cost?

Cheers

Kris

Several possibilities.

(i) the cold water is sitting in uninsulated pipes in the roof and
getting pretty hot.

(ii) you have a connection between hot and cold somewhere..possibilities
include an overheating tank that is forcing hot water back into the cold
feed, a faulty mixer tap that is on, but with the outlet blocked..and so on

(iii) The tank itself is faulty.