Hi everyone,

I had a plumber round a few weeks ago to fix an overflowing central
heating tank in the loft. I was in a hurry, so he just fitted an
isolating valve to the inlet and turned off the cold water supply. He
also removed some of the water from the tank, but said that the water
in the tank was very hot which shouldn't happen.

I've left the isolating valve switched off, but the pump has begun
making a lot of noise, so I went up in the loft, and the central
heating tank had run dry... I have now let more water into it.
However, before I fork out loads on a plumber, I have a couple of
questions:

1. Why is the water in the central heating tank getting so hot (there
was steam coming off it)
2. Why is the tank running dry so quickly... I would have thought
water loss from the system should be relatively low - but half the
tank has been emptied by it in 3 weeks.

What could the problem be and how much will it cost a professional to
fix it?

Any answers much appreciated.

Ian

In message
, Ian
Waddell wrote
Hi everyone,

I had a plumber round a few weeks ago to fix an overflowing central
heating tank in the loft. I was in a hurry, so he just fitted an
isolating valve to the inlet and turned off the cold water supply. He
also removed some of the water from the tank, but said that the water
in the tank was very hot which shouldn't happen.

I've left the isolating valve switched off, but the pump has begun
making a lot of noise, so I went up in the loft, and the central
heating tank had run dry... I have now let more water into it.
However, before I fork out loads on a plumber, I have a couple of
questions:

1. Why is the water in the central heating tank getting so hot (there
was steam coming off it)
2. Why is the tank running dry so quickly... I would have thought
water loss from the system should be relatively low - but half the
tank has been emptied by it in 3 weeks.

What could the problem be and how much will it cost a professional to
fix it?

Any answers much appreciated.


One reason could be is that the pump speed is too high and is pumping
hot water up the expansion pipe back into the tank. Hot water in a cold
loft will evaporate fast.

--
Alan
news2006 {at} amac {dot} f2s {dot} com

Rodney, where is the isolating valve, on the cold feed into the header
tank? if so this should NOT BE TURNED OFF, no wonder the tank's
running dry, not to mention dangerous. It is designed so the system
can expand into this tank through the vent pipe which hooks over the
top of the tank. Are all the radiators hot? If not there could be a
blockage causing the pump to pump up the vent pipe into the tank or up
the feed into the tank. How hot are the radiators getting, ie is it
boiling up. The cold feed into your tank should NOT be isolated.
This tank should normally be about 1/3rd full with the ball valve
adjusted to that level for precisely the above reason, so hot water
can expand into it without causing it to overflow. If switching the
isolator on causes it to overfill your ball valve needs adjusting or
has gone.
I also assume you are talking about your heating header tank which is
the smaller of the 2 tanks in your loft in most systems.

On 18 Mar, 21:59, wrote:
Rodney, where is the isolating valve, on the cold feed into the header
tank? if so this should NOT BE TURNED OFF, no wonder the tank's
running dry, not to mention dangerous. It is designed so the system
can expand into this tank through the vent pipe which hooks over the
top of the tank. Are all the radiators hot? If not there could be a
blockage causing the pump to pump up the vent pipe into the tank or up
the feed into the tank. How hot are the radiators getting, ie is it
boiling up. The cold feed into your tank should NOT be isolated.
This tank should normally be about 1/3rd full with the ball valve
adjusted to that level for precisely the above reason, so hot water
can expand into it without causing it to overflow. If switching the
isolator on causes it to overfill your ball valve needs adjusting or
has gone.
I also assume you are talking about your heating header tank which is
the smaller of the 2 tanks in your loft in most systems.

Yes, I'm talking about the heating header tank. I have turned the
isolating valve back on, but as I understand it, the water in the
header tank should not be getting hot. All the radiators get hot, so
I don't think there's a blockage anywhere. The boiler makes a
knocking noise - so could there be air trapped in the system that
means the expansion makes the vent pipe overflow back into the header
tank?

so is the tank still overflowing or is it sitting at about 1/3rd full
is the hot water coming into the tank through the vent pipe over the
top or the feed pipe at the bottom of the tank?
how hot are the radiators getting, hotter than usual, is it boiling up
= boiler thermostat gone?
try draining some out of a drain c*ck and make sure the header tank
starts filling up, this will check for a blocked feed from the tank
has anything changed with the pump, could be overpumping and needs
pump speed turning down

On 18 Mar, 22:14, wrote:
so is the tank still overflowing or is it sitting at about 1/3rd full
is the hot water coming into the tank through the vent pipe over the
top or the feed pipe at the bottom of the tank?
how hot are the radiators getting, hotter than usual, is it boiling up
= boiler thermostat gone?
try draining some out of a drain c*ck and make sure the header tank
starts filling up, this will check for a blocked feed from the tank
has anything changed with the pump, could be overpumping and needs
pump speed turning down

The tank isn't still overflowing.... I think that was caused by a
sticky float valve. I guess I'll need to hang around in the loft and
check whether the hot water is coming through the vent pipe or through
the feed pipe... or both! I don't think the boiler is over-heating as
it does shut off when it reaches temperature. The rads aren't any
hotter than you'd expect.... worried about the knocking noise from the
boiler though... it's overdue a service I think so I probably need to
get a Corgi round to have a look at that.

"Ian Waddell" wrote in message
...
On 18 Mar, 21:59, wrote:
Rodney, where is the isolating valve, on the cold feed into the header
tank? if so this should NOT BE TURNED OFF, no wonder the tank's
running dry, not to mention dangerous. It is designed so the system
can expand into this tank through the vent pipe which hooks over the
top of the tank. Are all the radiators hot? If not there could be a
blockage causing the pump to pump up the vent pipe into the tank or up
the feed into the tank. How hot are the radiators getting, ie is it
boiling up. The cold feed into your tank should NOT be isolated.
This tank should normally be about 1/3rd full with the ball valve
adjusted to that level for precisely the above reason, so hot water
can expand into it without causing it to overflow. If switching the
isolator on causes it to overfill your ball valve needs adjusting or
has gone.
I also assume you are talking about your heating header tank which is
the smaller of the 2 tanks in your loft in most systems.

Yes, I'm talking about the heating header tank. I have turned the
isolating valve back on, but as I understand it, the water in the
header tank should not be getting hot. All the radiators get hot, so
I don't think there's a blockage anywhere. The boiler makes a
knocking noise - so could there be air trapped in the system that
means the expansion makes the vent pipe overflow back into the header
tank?


Goes to show that plumbers might be able to bend and fix pipes - but they
don't all know how a heating system needs to operate.

Good luck.

"Ian Waddell" wrote

Hi everyone,

I had a plumber round a few weeks ago to fix an overflowing central
heating tank in the loft. I was in a hurry, so he just fitted an
isolating valve to the inlet and turned off the cold water supply. He
also removed some of the water from the tank, but said that the water
in the tank was very hot which shouldn't happen.

I've left the isolating valve switched off, but the pump has begun
making a lot of noise, so I went up in the loft, and the central
heating tank had run dry... I have now let more water into it.
However, before I fork out loads on a plumber, I have a couple of
questions:

1. Why is the water in the central heating tank getting so hot (there
was steam coming off it)
2. Why is the tank running dry so quickly... I would have thought
water loss from the system should be relatively low - but half the
tank has been emptied by it in 3 weeks.

What could the problem be and how much will it cost a professional to
fix it?

Any answers much appreciated.

The header tank can get warm-to-hot in normal operation due to expansion of
the contents of the system.
The loft temperature would have to be seriously cold though for this to
result in "steam" being visible IMHO.
Important to discover whether water is being "pumped over" the vent as
others have said. This will introduce air into the system and increase the
chance of sludge forming.
No issues with trying the pump speed lower, as long as the system performs
adequately afterwards (you can always turn it back up). Best to carefully
note any changes you make. Particularly if you close or open any valves,
note how many turns you change them by.

Phil