I'm trying to sort out a "no hot water" problem when boiler is set to
heat "hot water only, central heating off". Just get normal flows of
cold water from all the hot water taps.
The hot water flow pipe going into cylinder from boiler is very hot,
the return pipe coming out of the cylinder to the boiler is luke warm
where it exits cylinder.
The cylinder itself (including top) feels cold everywhere.
The boiler fires up but goes off after few minutes (say every 5
minutes).
I can hear water swishing through the pump which is running.

Its a conventional indirect system, Potterton Fuelsaver 65F boiler,
cylinder on first floor, expansion tank in loft (which is full).

I thought this was an airlock in the cylinder in the non-coil part of
cylinder, so attached hose & forced water out through cylinder out of
vent pipe, left it coming out for say 5 minutes & thought this would
be enough time to clear any air.
As this didnt fix problem,my question is how much water might need to
be forced through hose,cylinder & out vent pipe to get rid of air
lock. Might I need to replace the entire cylinder contents. I went
onto think the problem is now in the coil boiler fed part of the
cylinder but its hot going into the cylinder coil.
Help...
Steve

wrote in message
...
I'm trying to sort out a "no hot water" problem when boiler is set to
heat "hot water only, central heating off". Just get normal flows of
cold water from all the hot water taps.
The hot water flow pipe going into cylinder from boiler is very hot,
the return pipe coming out of the cylinder to the boiler is luke warm
where it exits cylinder.

Then clearly there isn't any flow through the coil. The water wouldn't drop
from very hot to lukewarm. The pipe going in is probably just hot from
conduction further down. The zone valve for hot water is probably stuck in
the closed position.

I thought this was an airlock in the cylinder in the non-coil part of
cylinder,

How could it possibly be an airlock? If there was no water in the cylinder
what would be cooling down the water in the coil pipe from very hot to
lukewarm? Doh!
--
Dave Baker

wrote in


I'm trying to sort out a "no hot water" problem when boiler is set to
heat "hot water only, central heating off".

The hot water/central heating options are acheived by a diverter valve that
controls which parts of your system gets to have the heated water flow
through it. It sounds to be quite possible that your diverter valve has
failed.

There are two main components to the valve - (1) the body which has the
inlet/outlet ports and the valve that opens and closes the flow in the ports
and (2) the actuator that moves the spindle of the valve, thus opening and
closing the ports.

Most valves (£40-£80) are relatively easy to replace:

compression fittings: loosen, remove old valve, replace with new valve,
tighten

wiring: remove wires from old valve and replicate layout for new valve.

Job done.

And sometimes it's even easier:

The problem is sometimes caused by the valve becoming stuck - occasionally,
with the actuator removed, the spindle of the valve can be persuaded to move
by encouraging it with a careful to-and-fro twist using a wrench.

Then again the problem can be the motor - this can usually be replaced
separately for about £25

Examples of complete valves, valve bodies, actuators and motors he

http://www.uk-plumbing.com/heating-c...c-220_274.html

--
PeterMcC
If you feel that any of the above is incorrect,
inappropriate or offensive in any way,
please ignore it and accept my apologies.

In an earlier contribution to this discussion,
wrote:

I'm trying to sort out a "no hot water" problem when boiler is set to
heat "hot water only, central heating off". Just get normal flows of
cold water from all the hot water taps.
The hot water flow pipe going into cylinder from boiler is very hot,
the return pipe coming out of the cylinder to the boiler is luke warm
where it exits cylinder.
The cylinder itself (including top) feels cold everywhere.
The boiler fires up but goes off after few minutes (say every 5
minutes).
I can hear water swishing through the pump which is running.

Its a conventional indirect system, Potterton Fuelsaver 65F boiler,
cylinder on first floor, expansion tank in loft (which is full).

I thought this was an airlock in the cylinder in the non-coil part of
cylinder, so attached hose & forced water out through cylinder out of
vent pipe, left it coming out for say 5 minutes & thought this would
be enough time to clear any air.
As this didnt fix problem,my question is how much water might need to
be forced through hose,cylinder & out vent pipe to get rid of air
lock. Might I need to replace the entire cylinder contents. I went
onto think the problem is now in the coil boiler fed part of the
cylinder but its hot going into the cylinder coil.
Help...
Steve

One thing is certain - you *don't* have an airlock in the DHW system
itself - otherwise you's get *nothing* rather than cold water out of the hot
taps.

For whatever reason, you have insufficient flow through the *primary*
circuit (boiler, pump, coil inside HW cylinder) to heat the water in the
tank. So the boiler fires for a little while, and then turns off on its
(internal) stat because the heat produced isn't being transferred to the
cylinder.

Could you give us a bit more detail about your system - particularly what is
supposed to control it. If the pump is running on HW-only, that suggestes
that it's a fully pumped system rather than gravity HW and pumped CH. Is
that your understanding? If this is so, there are likely to be one ore more
motorised valves in the system - probably (though not necessarily) in the
airing cupboard near the hot cylinder. How many are there - and what type?
[Likely to be one 3-port valve or two 2-port valves].

Is there a cylinder thermostat (as part of the controls for the
boiler/valve(s), *not* the one inside any immersion heater which may be
present)? Does it click when you turn it back and forth? What temperature is
it currently set at?

Is there a gate valve - or somesuch - on the output pipe from the cylinder
coil (i.e. the boiler return pipe)? If so, is it open?

You say that the expansion tank is full (that's the *little* tank which acts
as a header for the primary circuit, right?) Is there a tap or gate valve on
the pipe coming out of the bottom of that, which feeds the primary circuit?
If so, is it open?

You started by saying that this problem occurs when on HW-only with CH off.
What happens if you turn the CH on - do you then get get both CH *and* HW?
[I know you don't *want* the CH on this tgime of the year, but a quick test
may help to isolate the problem].
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Thanks very much gents, (I can forget the airlock blind alley &
disconnect the hose).

There is only 1 motorised valve (2 port) which is on a pipe going to
the rads & is not in the flow going into the Cylinder.
(The MV seems OK as its cold when HW is On & CH is Off, its hot when
CH is on)


BleedValve
I
HWCyl-----TRV-----------------I--------------
I I
I I
______I MV
I I I
I I I--- ToRads
GV1 I
I I
I I----------
HWCyl--- V1---------- I
I
I
I Pump VentPipe
_____I I I
I I I--------------------------
I FeedfromExpTank
I I
I I
I I
I--------------------------------------------I
I I I
I I
Boiler From Boiler
Return


Water flows from pump to Cylinder & Rads.
There is a thermostat on the cylinder which is connected via copper
wire to the ThermostaticRadiatorValve (TRV) on the pipe flowing into
Cylinder coil from Boiler. Ive set it to Max & it is working.
(Switching it to Max immediately causes it to get v hot including pipe
after it into cylinder. Doesnt this suggest there is NOT a full
blockage in the cylinder coil otherwise there would be no where for
the water to go & it wouldnt get hot immediately )

The valve (V1) on the output pipe from the cylinder coil is open. It
isnt a gate valve, more like a radiator valve with a square head you
need to turn with spanner to open & close.
There is no valve on the pipe run from the Expansion tank bottom
outlet.

When CH is set to on, it also does NOT heat the water in the cylinder
to normal hot temperature. (Only lukewarm after very long time)

GateValve (GV1) is open. (Not sure why its there, this pipe run seems
to short circuit the Cylinder, why would water flow through cylinder
coil when it can short circuit here.

Probably not relevant but the Cylinder coil inlet pipe entry point is
less than a third of Cylinder height from bottom. Seems low to me but
thats how it was made.

Hope you can draw some conclusions from this lot! thanks again
Steve

RESEND (diagram realignment only difference)

Thanks very much gents, (I can forget the airlock blind alley &
disconnect the hose).

There is only 1 motorised valve (2 port) which is on a pipe going to
the rads & is not in the flow going into the Cylinder.
(The MV seems OK as its cold when HW is On & CH is Off, its hot when
CH is on)


BleedValve
I
HWCyl-----TRV---------I--------------
I I
I I
____I MV
I I I
I I I--- ToRads
GV1 I
I I
I I--------
HWCyl--- V1----- I
I
I
I Pump VentPipe
_____I I I
I I I--------------------------
I FeedfromExpTank
I I
I I
I I
I--------------------------------------------I
I I I
I I
Boiler From Boiler
Return


Water flows from pump to Cylinder & Rads.
There is a thermostat on the cylinder which is connected via copper
wire to the ThermostaticRadiatorValve (TRV) on the pipe flowing into
Cylinder coil from Boiler. Ive set it to Max & it is working.
(Switching it to Max immediately causes it to get v hot including pipe
after it into cylinder. Doesnt this suggest there is NOT a full
blockage in the cylinder coil otherwise there would be no where for
the water to go & it wouldnt get hot immediately )

The valve (V1) on the output pipe from the cylinder coil is open. It
isnt a gate valve, more like a radiator valve with a square head you
need to turn with spanner to open & close.
There is no valve on the pipe run from the Expansion tank bottom
outlet.

When CH is set to on, it also does NOT heat the water in the cylinder
to normal hot temperature. (Only lukewarm after very long time)

GateValve (GV1) is open. (Not sure why its there, this pipe run seems
to short circuit the Cylinder, why would water flow through cylinder
coil when it can short circuit here.

Probably not relevant but the Cylinder coil inlet pipe entry point is
less than a third of Cylinder height from bottom. Seems low to me but
thats how it was made.

Hope you can draw some conclusions from this lot! thanks again
Steve




Thanks very much gents, (I can forget the airlock blind alley &
disconnect the hose).

There is only 1 motorised valve (2 port) which is on a pipe going to
the rads & is not in the flow going into the Cylinder.
(The MV seems OK as its cold when HW is On & CH is Off, its hot when
CH is on)


BleedValve
I
HWCyl-----TRV-----------------I--------------
I I
I I
______I MV
I I I
I I I--- ToRads
GV1 I
I I
I I----------
HWCyl--- V1---------- I
I I
I Pump VentPipe
___I I I
I I I----------------------I
FeedfromExpTank
I I
I I
I I
I------------------------------------I
I I I
I I
Boiler From Boiler
Return


Water flows from pump to Cylinder & Rads.
There is a thermostat on the cylinder which is connected via copper
wire to the ThermostaticRadiatorValve (TRV) on the pipe flowing into
Cylinder coil from Boiler. Ive set it to Max & it is working.
(Switching it to Max immediately causes it to get v hot including pipe
after it into cylinder. Doesnt this suggest there is NOT a full
blockage in the cylinder coil otherwise there would be no where for
the water to go & it wouldnt get hot immediately )

The valve (V1) on the output pipe from the cylinder coil is open. It
isnt a gate valve, more like a radiator valve with a square head you
need to turn with spanner to open & close.
There is no valve on the pipe run from the Expansion tank bottom
outlet.

When CH is set to on, it also does NOT heat the water in the cylinder
to normal hot temperature. (Only lukewarm after very long time)

GateValve (GV1) is open. (Not sure why its there, this pipe run seems
to short circuit the Cylinder, why would water flow through cylinder
coil when it can short circuit here.

Probably not relevant but the Cylinder coil inlet pipe entry point is
less than a third of Cylinder height from bottom. Seems low to me but
thats how it was made.

Hope you can draw some conclusions from this lot! thanks again
Steve

wrote:
RESEND (diagram realignment only difference)

Sorry, still no good. You need to make sure you're using a fixed-width
(not proprtional) font when you create such diagrams. I think "Courier
New" is the traditional one on Windows?

Pete

In an earlier contribution to this discussion,
wrote:

Thanks very much gents, (I can forget the airlock blind alley &
disconnect the hose).

There is only 1 motorised valve (2 port) which is on a pipe going to
the rads & is not in the flow going into the Cylinder.
(The MV seems OK as its cold when HW is On & CH is Off, its hot when
CH is on)


BleedValve
I
HWCyl-----TRV-----------------I--------------
I I
I I
______I MV
I I I
I I I--- ToRads
GV1 I
I I
I I----------
HWCyl--- V1---------- I
I
I
I Pump VentPipe
_____I I I
I I I--------------------------
I FeedfromExpTank
I I
I I
I I
I--------------------------------------------I
I I I
I I
Boiler From Boiler
Return


Water flows from pump to Cylinder & Rads.
There is a thermostat on the cylinder which is connected via copper
wire to the ThermostaticRadiatorValve (TRV) on the pipe flowing into
Cylinder coil from Boiler. Ive set it to Max & it is working.
(Switching it to Max immediately causes it to get v hot including pipe
after it into cylinder. Doesnt this suggest there is NOT a full
blockage in the cylinder coil otherwise there would be no where for
the water to go & it wouldnt get hot immediately )

The valve (V1) on the output pipe from the cylinder coil is open. It
isnt a gate valve, more like a radiator valve with a square head you
need to turn with spanner to open & close.
There is no valve on the pipe run from the Expansion tank bottom
outlet.

When CH is set to on, it also does NOT heat the water in the cylinder
to normal hot temperature. (Only lukewarm after very long time)

GateValve (GV1) is open. (Not sure why its there, this pipe run seems
to short circuit the Cylinder, why would water flow through cylinder
coil when it can short circuit here.

Probably not relevant but the Cylinder coil inlet pipe entry point is
less than a third of Cylinder height from bottom. Seems low to me but
thats how it was made.

Hope you can draw some conclusions from this lot! thanks again
Steve

As someone else has said, even your MkII ASCII art isn't very clear - it
needs to use a fixed width font.

Meanwhile, you said that when setting the controls to HW+CH, the HW *still*
doesn't get hot. But you didn't say whether the radiators get hot. Do they?
If so, that would eliminate the pump. If not, the pump has to be the prime
suspect - its impellor could have become detached from the shaft so that,
although the motor is running, it ain't doing any pumping.

The pipe and gate valve which is in parallel with the cylinder coil is
probably a by-pass circuit - to provide a flow path even when then TRV is
closed. Have you tried partially closing it, to give a bit more urge to the
water going through the coil? Could someone have inadvertently fiddled with
it - causing your problem?

Now would be a good time to overhaul your CH system, and install some proper
controls which provide a boiler interlock. You could save a *lot* of gas.
When was the system installed - as far as I know, the setup you describe
hasn't been common in new installs for a good many years?
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Thanks again, (sorry about the diagram-it still might not be clear but
hopefully lines up and clearer than trying to put into words)


BleedValve
I
HWCyl-----TRV-----------------I-------------I
I I
I I
______I MV
I I I
I I I---ToRads
gV1 I
I I
I I----------
HWCyl--- V1-------------I I
I I
I Pump VentPipe
_____I I I
I I I-----------------I
I I I
I I I FeedfromExpTank
I I I I
I I I------------------------I
I I I
I I
Boiler From
Return Boiler



The system is about 20 years old (just bought the house).
The rads do get hot when CH (& CH+HW) set to on.
The Gatevalve (gV1) is fully open. I did actually close it fully in
trepidation (but reasoned the boiler shouldnt explode fingers crossed.
Still the same- luke warm at HWCyl - V1 , the boiler forced up hot
water through the vent pipe and stopped, so at least that bits
working!)
I am wondering could there be air in this boiler feed / boiler
return / cylinder coil circuit that would cause this problem so that
the pump is unable to pump effectively to & through coil.
How probable is it that valve (V1) is partially blocked, or God forbid
the cylinder coil itself.
Or could the pump itself not be pumping at a high enough pressure.
What does it mean if there is still no hot water coming out of coil
even when the Gatevalve (gV1) is fully closed.

The CH overhaul sounds like a good idea, I just wish it was an easy (&
quick) job.
Thanks
Steve