Immersion Vs Boiler

realflash17

Hoping you plumbing experts might be able to offer some advice.

In a rented house and there are two ways of heating the hot water.

Using the boiler on its own heats the water very quickly, 30 minutes and it is piping hot, enough to fill a bath easily, but I find the boiler heavy on oil.


The other way is an immersion, but if I stick it on for an hour I find the water is luke warm, what I noticed is that there is a hot water pump switch right beside the immersion, does this need to be turned on at the same time as the immersion all the time or what does it do? When I switch both on, the results are very good.

Just not sure what exactly the pump does, and why would it be just built into the immersion switch if both need to run together.

Pic attached.

Appreciate any advice.

John.G

realflash17 wrote: »

Hoping you plumbing experts might be able to offer some advice.

In a rented house and there are two ways of heating the hot water.

Using the boiler on its own heats the water very quickly, 30 minutes and it is piping hot, enough to fill a bath easily, but I find the boiler heavy on oil.


The other way is an immersion, but if I stick it on for an hour I find the water is luke warm, what I noticed is that there is a hot water pump switch right beside the immersion, does this need to be turned on at the same time as the immersion all the time or what does it do? When I switch both on, the results are very good.

Just not sure what exactly the pump does, and why would it be just built into the immersion switch if both need to run together.

Pic attached.

Appreciate any advice.

Where is the immersion element (or elements) located in cylinder?. Have you another switch somewhere labeled "Sink" & "Bath"?

Re: The hot water pump switch, this may turn on another pump that circulates water around the house and returns it to the cylinder via a secondary connection. It saves water by ensuring that you have hot water available at the various draw off points. I dont know why it should improve the immersion performance though, generally there can be a heat loss when using this pump, depending on the pipework insulation. If this pump isnt on, then, especially in the morning, you might have to run off 5 to 10 litres of water before it reaches its fully hot temperature.

realflash17

No other switch to alternate between bath or sink. Unable to tell you where the element is but based on the noise i would be sure it is in the cylinder. It is a fairly modern looking heating tank system not your traditional copper tank, the landlord previously described it as a tank within a tank so it keep the water warm for a long time.
Re: the the hot water pump, I am stumped . Perhaps you are right it sends the heated water around to draw off points quickly, and rather than it seemingly helping the immersion to heat the water faster, it might just get the results to us faster than when it is not on thereby giving the impression it is heating the water quicker.
I tried a few different combinations over the weekend, I have came to the conclusion that it will only heat the water well  when the oil burner is heating it.

John.G

If its a "tank in tank" cylinder then its more than likely that there is a 3 Kw electric element in the bottom of the cylinder, you said in your first post that the oil will heat up the cylinder in 30 minutes, assuming that you have a 150 litre cylinder then this makes sense as it will take 8.7 Kwh to heat the water from say cold, 10C, to 60C. If a 3 Kw "immersion" is only on for 1 hour then this will only heat the water to around 30C (barely lukewarm). the immersion would have to be on for around 3 hrs in order to heat the water to 60C (from 10C).
You also stated that you found the boiler heavy on oil, well assuming that you only use it once per day (in the summer) and assuming system contents of 30 litres (radiators zoned and off) and a boiler efficiency of say a minimum of 75%, then you will be heating 180 litres (150+30) which should require about 13.95 Kwh (boiler input) or about 1.33 litres of oil at a cost of €0.93/day with oil at 70C/litre. The Immersion using full cost power at say €0.18/Kwh and with 100% efficiency will consume 8.7 Kwh and cost around €1.57/day. This means (if the calcs are correct) that the boiler efficiency would have to be as low as 44% to cost as much as full cost elec power. If you have night rate power then the immersion would be cheaper to use if the water is only heated at night.

realflash17

Thanks a million for the very detailed reply. I guess I have never ran the boiler on its own without the rads but now that the warmer weather has arrived I will be able to just heat the water alone with the oil and it might actually be grand and not as heavy as I first thought on fuel.
thanks again