[meldrewreborn]

@geoffers

My hot water tank (non mega flow) is heated morning and evening for set times and once the desired temperature is reached the system switches off. I doubt that in any system the boiler fires all day. If it were set to operate any time of the day it would fire intermittently as tank losses and water draw off lower the temperature of the stored water.. Similarly, in a combi I've seen them fire intermittently to maintain the internal mini tank temperature, so producing near instant hot water at nearby taps.

What you describe of using the immersion morning and evening is essentially the same as my practice. The headline price of electricity is nearly 5 times the price of gas, and I'd aimed off for boiler and pipework losses in stating 4 times as a rule of thumb.

[geoffers]

@meldrewreborn 👍 - but for me, my point was that on the N.D. tariff I can use the midnight to 7am. rate to use the electricity at less than ⅓ the cost of the daytime rate.

[meldrewreborn]

@geoffers

Your link is quite interesting.

I can remember the panic caused by the reportedly unknown disease that struck down hundreds of veterans after a meeting in 1976. Eventually the causes were identified and action taken to prevent a repeat.

The story in Wiki is revealing:

1976 Philadelphia Legionnaires' disease outbreak - Wikipedia

But of course the offending organisms had been around for millennia and it was primarily changes in the way we use water that led to the first identified outbreak and its cause.

[meldrewreborn]

Originally Posted by geoffers

@meldrewreborn 👍 - but for me, my point was that on the N.D. tariff I can use the midnight to 7am. rate to use the electricity at less than ⅓ the cost of the daytime rate.

Agree in full.

[geoffers]

Originally Posted by meldrewreborn

@geoffers

My hot water tank (non mega flow) is heated morning and evening for set times and once the desired temperature is reached the system switches off. I doubt that in any system the boiler fires all day. If it were set to operate any time of the day it would fire intermittently as tank losses and water draw off lower the temperature of the stored water.. Similarly, in a combi I've seen them fire intermittently to maintain the internal mini tank temperature, so producing near instant hot water at nearby taps.

What you describe of using the immersion morning and evening is essentially the same as my practice. The headline price of electricity is nearly 5 times the price of gas, and I'd aimed off for boiler and pipework losses in stating 4 times as a rule of thumb.

I'd actually only scheduled my immersion to come on for ½ hour @6:30 a.m so it clearly wasn't hitting the 60⁰C thermostat setting as it was consistently using about 1.7kWh of energy every morning.

In the interests of science (and having read that article on legionella) I have now set the immersion scheduler to run for a full hour from 6:00 a.m.

Bright shows the first half hour taking 1.71 kWh (cost=16p), then during the second half hour it only used 0.62 kWh before it must have hit the thermostat switch off. So a further 6p to get to 60°C (obviously dependent on the starting temperature of the water)

I'll run it like this for a few more days as a control, then set the gas boiler to do the same to get a comparative costing 👍

[TAYLOROY]

@geoffers

Great idea, please keep us updated, I’m switching to ev tariff soon and would love to see the price comparison between gas and electricity for heating hot 2 water at the cheaper rate.

[meldrewreborn]

@geoffers

I’m a great believer in measuring - as without proper data we’re either estimating (based on known source information) or guessing.

However, we’re all different and our thresholds for making a decision on whether a measurement is necessary will vary, and our access to measuring capable equipment will vary too.

[geoffers]

Originally Posted by TAYLOROY

@geoffers

Great idea, please keep us updated, I’m switching to ev tariff soon and would love to see the price comparison between gas and electricity for heating hot 2 water at the cheaper rate.

I'll certainly keep you posted 👍

FYI if you do consider scheduling your immersion heater using the cheap rate leccy, you might want to consider one of these smart immersion switches.... https://www.amazon.co.uk/gp/aw/d/B0C3HJ2Y4B

I've wired mine in the circuit after the actual immersion switch so leave the immersion switch on, but use the smart switch to schedule the actual on time. You can also use your phone, "Hey Google", Alexa etc etc to toggle the immersion on/off 👍

[JoeSoap]

As the Megaflo has been mentioned, I have just finished regenerating the air gap in mine. It takes about 15-20 minutes from start to finish.
@sbsmiths is there any further news on your problem. Has it now gone away?

[geoffers]

↵

Originally Posted by TAYLOROY

@geoffers

Great idea, please keep us updated, I’m switching to ev tariff soon and would love to see the price comparison between gas and electricity for heating hot 2 water at the cheaper rate.

@TAYLOROY @meldrewreborn

I ran the gas h/w only test for 1½hrs taking before and after meter readings which showed 0.542m³ usage - doing the maths 0.542 x 38.9 (calorific value) x 1.02264 / 3.6 = 5.989kWh

So based on my kWh usage of 5.989 @ 7.4p this cost 44.32p

Running my 3kW immersion until it reached the thermostat temperature took 2.33kWh

So on the Next Drive tariff of 9.5p this cost 22.13p, which is half the cost of heating by gas.

However on a standard tariff rate of say 28p this would have cost 65.24p which is about 50% more than using gas.

It appears that (although being more expensive on the standard rate) heating by electricity is clearly nearly three times more efficient energy wise than heating by gas!

Interesting - I started the hot water test @ around 6 a.m (c/h was set to off) expecting to see the system/pump stop when the tank water reached 60⁰C

The light on the pump never went off, so the pump appeared to be on the whole time, so I terminated the test @ 7:30

I've got an old spring-mounted c/h thermometer on the boiler feed pipe which indicated ~145⁰F = 63⁰C (not sure how accurate this is)

Although the boiler must have cycled off, with the pump running for the whole period the boiler feed temperature was showing ~130⁰F=54⁰C. Since the pump was still circulating the feed-water, this must indicate the feed temperature is now being maintained by the h/w in the tank.

Worryingly, this situation would gradually cause the h/w tank temperature to drop as the tank heat-exchanger would now be losing heat to the circulating feed rather than gaining it from the boiler.

I'm sure the wiring of the controller should cause the h/w valve to close when the tank thermostat reaches temperature, and if the c/h isn't active also turns the boiler off, so would also expect the pump to stop in this situation