The water pressure in my domestic hot water supply has recently dropped to
very low levels. The water temperature is fine and there is no problem
with the cold water supply. When I open a hot water tap anywhere in the
house, the water dribbles out for a while and then suddenly gushes for a
couple of seconds and then reverts to the dribble. I have an oil fired
furnace and a tankless water heater, and when I had a serviceman out
recently for another problem, I described the low pressure problem and
asked him if the low pressure could be caused by something in the
furnace/tankless system. He told me that as long as I had hot water, the
pressure problem wouldn't be in the furnace/water heater, and I should call
a plumber. I'm willing to do that, but before I do I thought I'd ask if
anyone in the NG had any idea of what might be happening. Any ideas?

On Sunday, February 17, 2019 at 5:07:32 AM UTC-5, Alan Holbrook wrote:
The water pressure in my domestic hot water supply has recently dropped to
very low levels. The water temperature is fine and there is no problem
with the cold water supply. When I open a hot water tap anywhere in the
house, the water dribbles out for a while and then suddenly gushes for a
couple of seconds and then reverts to the dribble. I have an oil fired
furnace and a tankless water heater, and when I had a serviceman out
recently for another problem, I described the low pressure problem and
asked him if the low pressure could be caused by something in the
furnace/tankless system. He told me that as long as I had hot water, the
pressure problem wouldn't be in the furnace/water heater, and I should call
a plumber. I'm willing to do that, but before I do I thought I'd ask if
anyone in the NG had any idea of what might be happening. Any ideas?

Are you sure that serviceman said that the problem couldn't be in the
tankless or the furnace? Or was he a furnace serviceman and he just said it's
not in the furnace? The latter would make sense, if it really is a
furnace and not a boiler that also heats your water. A furnace has nothing
to do with hot water. A tankless sure does. Since it's in all outlets,
then it's a problem with the flow into the tankless, the tankless itself,
or after the tankless before the first faucet. Sounds like it's time to
call the plumber.

On 2/17/19 5:07 AM, Alan Holbrook wrote:
When I open a hot water tap anywhere in the
house, the water dribbles out for a while and then suddenly gushes for a
couple of seconds and then reverts to the dribble.


Do you have galvanized steel water pipes?

On 2/17/2019 5:07 AM, Alan Holbrook wrote:
The water pressure in my domestic hot water supply has recently dropped to
very low levels. The water temperature is fine and there is no problem
with the cold water supply. When I open a hot water tap anywhere in the
house, the water dribbles out for a while and then suddenly gushes for a
couple of seconds and then reverts to the dribble. I have an oil fired
furnace and a tankless water heater, and when I had a serviceman out
recently for another problem, I described the low pressure problem and
asked him if the low pressure could be caused by something in the
furnace/tankless system. He told me that as long as I had hot water, the
pressure problem wouldn't be in the furnace/water heater, and I should call
a plumber. I'm willing to do that, but before I do I thought I'd ask if
anyone in the NG had any idea of what might be happening. Any ideas?


What do you really have? Furnaces heat air, boiler heat water.

Just a guess, you have hot water heat and the boiler makes the water hot
for the heating system as well as hot water for domestic use. Inside
the box there is a coil of tubing that has the domestic hot water. They
can clog up over time and affect water pressure. If you have hard water
it can be loaded with minerals.

How old in the unit? Look at all the options/. The coil can be
replaced, but, it is foolish if the boiler is old and not very
efficient. In my last house I had a system like I just described. It
was having other problems so I replaced it with a System 2000 made by
www.energykinetics.com. It reduced my oil use by 39% and the savings
paid for it over 7 years. (yes, I tracked it by degree days) It has a
separate tank for holding the hot water and it gave all the hot water
you can ever use.

One more thing. Don't trust the guy that you had out for repairs, he
seems rather limited in knowledge.

On Sunday, February 17, 2019 at 4:07:32 AM UTC-6, Alan Holbrook wrote:
The water pressure in my domestic hot water supply has recently dropped to
very low levels. The water temperature is fine and there is no problem
with the cold water supply. When I open a hot water tap anywhere in the
house, the water dribbles out for a while and then suddenly gushes for a
couple of seconds and then reverts to the dribble. I have an oil fired
furnace and a tankless water heater...

Unless you have very "soft" water a tankless water heater requires
regular descaling to keep them from clogging up.

On Sun, 17 Feb 2019 04:07:23 -0600, Alan Holbrook wrote:

The water pressure in my domestic hot water supply has recently dropped to
very low levels.

Think about the difference between pressure and flow-rate.

Is your complaint really about pressure? Or is it about flow-rate? If it's about pressure,
what pressure have you measured?

If you measure the pressure, and it's 40 PSI or more, pressure is not your problem--something
is restricting the flow. Flow can be restricted, but pressure cannot--it can only be allowed
or not allowed.

--
croy

On 2/17/2019 7:38 PM, croy wrote:
On Sun, 17 Feb 2019 04:07:23 -0600, Alan Holbrook wrote:

The water pressure in my domestic hot water supply has recently dropped to
very low levels.

Think about the difference between pressure and flow-rate.

Is your complaint really about pressure? Or is it about flow-rate? If it's about pressure,
what pressure have you measured?

If you measure the pressure, and it's 40 PSI or more, pressure is not your problem--something
is restricting the flow. Flow can be restricted, but pressure cannot--it can only be allowed
or not allowed.

99% of the questions about water pressure are really flow rate. Once
the valve is opened, pressure drops considerably no matter the flow. I
bet the static pressure is the same on hot and cold but the hot is flow
restricted.

On Sun, 17 Feb 2019 22:17:05 -0500, Ed Pawlowski wrote:

99% of the questions about water pressure are really flow rate. Once
the valve is opened, pressure drops considerably no matter the flow. I
bet the static pressure is the same on hot and cold but the hot is flow
restricted.

Right. It's all about fluid dynamics.

--
croy