Reply With QuoteThe amount of hot water available will
depend on the size of the hot water tank. Unless it’s a Combi boiler?
I was chatting with my dad today and the conversation came around to heating as I’m currently in the middle of having a bathroom refit.
He has oil central heating but he told me that he can only fill his bath about a quarter full before the hot water runs cold. That can’t be right surely?
He had his boiler serviced recently by the same guy who fitted the oil central heating system and when he questioned it with the fitter, the fitter just suggested that he turn the hot water tap on less so the flow is slower.
I know nothing about central heating whether it be solid fuel, gas or oil, but what he explained to me doesn’t sound right.
I know there is a wide spectrum of intelligent members on here so I’m hoping someone has come across this before and can shed some light on the situation.
Cheers.
The amount of hot water available will
depend on the size of the hot water tank. Unless it’s a Combi boiler?
Sorry, should have said. Yes, it’s a combi boiler. He doesn’t have a water tank.Originally Posted by demonloop
Somethings not right there, and it’s not because it’s an oil fired system.
We use oil and most of the village I live in is the same. We are good for at least 4 baths! 😆
We use oil in the village where I live ( National Trust ), no baths, just showers and a small tank, but have constant hot water.
Nothing to do with oil, i can fill very hot baths easily with very fast flowing water. Either a poor system not fit for the home it is in or an issue somewhere.
A combi boiler gears the water as you are using if so there should be no issues. Gas or oil is just the medium getting burnt to provide heat.
If he’s having an issue then the boiler is not heating the water that’s flowing through the boiler so either the oil is not getting to the burners in sufficient quantity or there’s a safety overheat switch that’s shutting it down.
Either way, the boiler needs looking at.
Believe or not, but the advice that he got from the installer is correct.
Combi boilers can only heat a certain flow/volume of water (obviously). More importantly, they can only transfer a finite amount of energy (heat) into the flowing water. During the depths of winter, the ambient temperature of the water coming from the mains is so low (especially at the moment) that the combi boiler can’t transfer enough energy in order to heat it sufficiently.
The advice is correct - limit the flow and the temperature will go up.
(We had exactly the same issue with a combi boiler in a previous rental property. The boiler was regularly serviced and running as designed).
I was about to ask a similar question... one of my houses has fantastic cold water pressure at all taps, but the hot water is half the pressure, so much so that by the time you’ve filled a bath (20+ mins easily) it’s luke warm (even though the water at the tap is fully hot).
Am I right in presuming this is just an underpowered boiler?
The boiler was serviced only recently and also had a full system flush / magnatec etc
Oil central heating here, but with a pressurised system/hot water tank and no problem.
The fuel used in a combi shouldn’t make any difference. Sounds to me that either the boiler is to small or that it’s not burning effectively.
Whoever does not know how to hit the nail on the head should be asked not to hit it at all.
Friedrich Nietzsche
Most likely a boiler fault, lots of possibilities, perhaps a restriction in secondary heat exchanger, thermistor fault, passing down the heating at diverter valve? Would need investing to prove a diagnosis.
However, worth considering is if this is a new problem that has come to light during this recent bout of sub zero temperatures, we’ve had a few calls in the last couple of weeks for poor hot water.
A Combi boiler is designed to heat the temperature of the incoming cold mains by a minimum heat rise. e.g. if the incoming cold mains temperature is 4 degrees, the boiler may only have the capability to raise the temperature of the water by 35 degrees at a delivery rate of 11-12 litres per minute, if this is the case you may find that when running a bath at full rate you might only be getting hot water around the 40 degree mark?
One way to combat this in very cold conditions is indeed to reduce the flow from the tap, this keeps the cold water in the boiler longer before delivery, which increases the temperature of the hot water being delivered, the down side is this obviously takes longer to fill a bath.
Worth getting it checked.
Not the OP’s problem - he said he can fill part bath then it runs cold.
An underpowered boiler would fill the bath with consistently lukewarm water.
Nope. We had exactly the same. It would run hot initially and then it was as if ‘the boiler couldn’t keep up’. It is because of the ambient temperature of the cold water going into the boiler.
Try following the advice (run the hot tap slowly for the time being). The ‘problem’ will go away with Spring.
Yep this is how ours works , less of an issue in warmer weather when the central heating isnt working hard also
Combi boiler has a small internal tank that will be piping hot, so the first part of the water into the bath will be hot. The rest of the water won’t get hot at all. Luke warm at very best, for the reasons Bravo said
As above - it can be compared to the poor performance of many electric showers in these temperatures.
But - make sure that the HW temp setting is as high as it can go/you can stand from taps.
Yep, combi boiler has separate dials for CH and water - my pipes run under a suspended floor in an exposed location so I adjust dials probably May and Oct/Nov no issues after setting dials.
Last edited by Suds; 14th February 2021 at 20:37.
If it's like our gas boiler the internal tank is very small, just enough to provide hot water while the boiler is firing up. Certainly not enough to quarter fill a bath.
No, but there is probably enough cold(ish) water in the pipes that can be heated sufficiently by the boiler.
However, once the mains water from outside the property starts flowing, the temperature of that water is too low to be heated at full flow. Hence restricting the flow during the depths of winter.
Don't know if possible, but maybe install a separate tank. Electrical or oil powered and disconnect the smaller tank
My water tank has a knob for increasing the heat of the water (usually not recommended) that should make the water hotter to start
I'm in Canada, so things may be different and my system runs on gas
DON
Thank you all for the suggestions, I’ll pass them on to my dad.
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