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?
Hot Water Pressure Problem (2025 Update)
Feb 17, 2019
Last reply: 8 months ago
5 Replies
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.
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
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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.
Unless you have very "soft" water a tankless water heater requires regular descaling to keep them from clogging up.
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.
Right. It's all about fluid dynamics.
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