Hi,

Every few days when I get up to have my morning shower I find that the
hot water is not as hot as it should be so I need to adjust the shower
mixer. The water is heated by a gas boiler which is also used for the
central heating. The central heating appears to be fine and the hot
water is usually OK - I have this problem maybe one day every three or
four. I know it's not just the shower because the water from the taps is
also affected. Could it just be a dodgy thermostat on the hot water
tank, or perhaps something more sinister (and expensive)?

Cheers,
Grant

In an earlier contribution to this discussion,
Grant wrote:

Hi,

Every few days when I get up to have my morning shower I find that the
hot water is not as hot as it should be so I need to adjust the shower
mixer. The water is heated by a gas boiler which is also used for the
central heating. The central heating appears to be fine and the hot
water is usually OK - I have this problem maybe one day every three or
four. I know it's not just the shower because the water from the taps
is also affected. Could it just be a dodgy thermostat on the hot water
tank, or perhaps something more sinister (and expensive)?

Cheers,
Grant

You need to tell us a bit more about your system before we can give a
sensible answer.

Are both HW and CH circuits pumped, or does HW rely on gravity (convection)
circulation?

If fully pumped, how many motorised valves are there? [There will likely be
either one 3-port valve (Y-Plan) or two 2-port valves (S-Plan) - see
http://content.honeywell.com/uk/homes/systems.htm for details.]

If the HW uses gravity circulation, is there any sort of valve controlling
the flow? [You may have a 2-port motorised valve in the unlikely event that
you have a C-Plan system, or you may have a thermostatic valve such as a
Drayton Cyltrol (rather like a big thermosatic radiator valve)]

Is your system vented or sealed/pressurised? If vented, is there adequate
water in the small fill & expansion tank (not the large header tank) in the
attic? If pressurised, what are the pressures when the system is a) cold and
b) hot?
--
Cheers,
Set Square
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Set Square wrote:
In an earlier contribution to this discussion,
Grant wrote:


Hi,

Every few days when I get up to have my morning shower I find that the
hot water is not as hot as it should be so I need to adjust the shower
mixer. The water is heated by a gas boiler which is also used for the
central heating. The central heating appears to be fine and the hot
water is usually OK - I have this problem maybe one day every three or
four. I know it's not just the shower because the water from the taps
is also affected. Could it just be a dodgy thermostat on the hot water
tank, or perhaps something more sinister (and expensive)?

Cheers,
Grant


You need to tell us a bit more about your system before we can give a
sensible answer.

Are both HW and CH circuits pumped, or does HW rely on gravity (convection)
circulation?


I think they are both pumped. That is, I can hear a pump going when
either the HW or CH are on.

If fully pumped, how many motorised valves are there? [There will likely be
either one 3-port valve (Y-Plan) or two 2-port valves (S-Plan) - see
http://content.honeywell.com/uk/homes/systems.htm for details.]


I have no idea, which probably means I'll have to get an engineer to
have a look at this for me.

If the HW uses gravity circulation, is there any sort of valve controlling
the flow? [You may have a 2-port motorised valve in the unlikely event that
you have a C-Plan system, or you may have a thermostatic valve such as a
Drayton Cyltrol (rather like a big thermosatic radiator valve)]

Is your system vented or sealed/pressurised? If vented, is there adequate
water in the small fill & expansion tank (not the large header tank) in the
attic? If pressurised, what are the pressures when the system is a) cold and
b) hot?

It's a vented system. I have no idea about the small fill & expansion
tank. Is there an easy way to check that the water level is adequate?

Thanks for your reply, but it appears that I don't have enough
information for you!

Cheers,
Grant

In an earlier contribution to this discussion,
Grant wrote:

Set Square wrote:
In an earlier contribution to this discussion,
Grant wrote:


Are both HW and CH circuits pumped, or does HW rely on gravity
(convection) circulation?


I think they are both pumped. That is, I can hear a pump going when
either the HW or CH are on.

If fully pumped, how many motorised valves are there? [There will
likely be either one 3-port valve (Y-Plan) or two 2-port valves
(S-Plan) - see http://content.honeywell.com/uk/homes/systems.htm for
details.]


I have no idea, which probably means I'll have to get an engineer to
have a look at this for me.

You should be be able to find your motorised valves if you have any - most
likely in the airing cupboard, or possibly near the boiler. A 3-port valve
looks like http://tinyurl.com/arn5l (but not necessarily that way up). A
2-port valve is similar, but only has 2 water connections rather than being
T-shaped.

I would put my money on it being a 3-port valve - which has partially seized
due to sitting in the HW position all summer - and which is now sticking in
the CH position. But have a look and see what you can find.


It's a vented system. I have no idea about the small fill & expansion
tank. Is there an easy way to check that the water level is adequate?


The outlet pipe which feeds the system is at or very near to the bottom of
the tank. This must be covered at all times - otherwise air will be drawn
into the system and the water won't circulate properly. The level is
maintained by a ball-valve. These sometimes stick closed because they don't
have to open very often. Then, when the level drops due to a leak - or even
evaporation - the ball valve fails to operate, and you have a problem. If
the ball is above the water, and not floating in it, that would indicate
that it was stuck. If you just tap the ball very gently, you should hear a
hiss. Having said all of that, you don't want *too* much water in the tank -
otherwise it overflows when the system gets hot - causing another set of
problems!
--
Cheers,
Set Square
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If you have a timer controlling hot water heating, it could be this needs
changing, maybe to allow for British Summer Time hour change.
If someone baths late at night and the hot water heating doesn't come on
early enough, low temp water in the morning would be the likely outcome.

Phil

TheScullster wrote:
If you have a timer controlling hot water heating, it could be this needs
changing, maybe to allow for British Summer Time hour change.
If someone baths late at night and the hot water heating doesn't come on
early enough, low temp water in the morning would be the likely outcome.

Phil



The timer is set at the correct time and no-one has a bath late at
night. What seems to be happening is that on the mornings when the water
isn't as hot as usual, the boiler doesn't come for as long.

Set Square wrote:

You should be be able to find your motorised valves if you have any - most
likely in the airing cupboard, or possibly near the boiler. A 3-port valve
looks like http://tinyurl.com/arn5l (but not necessarily that way up). A
2-port valve is similar, but only has 2 water connections rather than being
T-shaped.

I would put my money on it being a 3-port valve - which has partially seized
due to sitting in the HW position all summer - and which is now sticking in
the CH position. But have a look and see what you can find.


It's a vented system. I have no idea about the small fill & expansion
tank. Is there an easy way to check that the water level is adequate?



The outlet pipe which feeds the system is at or very near to the bottom of
the tank. This must be covered at all times - otherwise air will be drawn
into the system and the water won't circulate properly. The level is
maintained by a ball-valve. These sometimes stick closed because they don't
have to open very often. Then, when the level drops due to a leak - or even
evaporation - the ball valve fails to operate, and you have a problem. If
the ball is above the water, and not floating in it, that would indicate
that it was stuck. If you just tap the ball very gently, you should hear a
hiss. Having said all of that, you don't want *too* much water in the tank -
otherwise it overflows when the system gets hot - causing another set of
problems!


Thank you very much for your help. I will have a look tonight.

Cheers,
Grant

Set Square wrote:

I would put my money on it being a 3-port valve - which has partially seized
due to sitting in the HW position all summer - and which is now sticking in
the CH position. But have a look and see what you can find.


Would this not mean that the radiators would get warm when the HW was
on? We don't have the CH turned on in the mornings at the moment and the
radiators are stone cold even on the days that the HW is not as warm as
it should be.

Cheers,
Grant

In an earlier contribution to this discussion,
Grant wrote:

Set Square wrote:

I would put my money on it being a 3-port valve - which has
partially seized due to sitting in the HW position all summer - and
which is now sticking in the CH position. But have a look and see
what you can find.


Would this not mean that the radiators would get warm when the HW was
on? We don't have the CH turned on in the mornings at the moment and
the radiators are stone cold even on the days that the HW is not as
warm as it should be.

Cheers,
Grant

Yes it would - so it's unlikely to be that then. [I had assumed that the
heating was on as well].

In that case, it sounds more like the cylinder thermostat telling porkies -
and turning the boiler and pump off before the water is hot. Check the stat
setting, and check whether it clicks on and off convincingly when you turn
it through the set point.
--
Cheers,
Set Square
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