[JoeSoap]

Originally Posted by geoffers

↵
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...

When I had this problem I realised that my boiler thermostat was set to a lower temperature than the hot water cylinder thermostat. That meant that the boiler could never satisfy the demand of the cylinder so the motorised valve to the tank coil stayed open and the pump kept running.

Once I set my tank thermostat to around 60-65 degrees and the boiler thermostat to around 80-85 degrees it cured the problem.

[geoffers]

Originally Posted by JoeSoap

When I had this problem I realised that my boiler thermostat was set to a lower temperature than the hot water cylinder thermostat. That meant that the boiler could never satisfy the demand of the cylinder so the motorised valve to the tank coil stayed open and the pump kept running.

Once I set my tank thermostat to around 60-65 degrees and the boiler thermostat to around 80-85 degrees it cured the problem.

Yep - figured that might be the case as the feed temperature was only marginally above the tank thermostat setting - will adjust & try again tomorrow 👍

[meldrewreborn]

@geoffers
on my system the live feed goes from the programmer to the tank thermostat. If store temperature is too low thermostat passes live feed to isolating valve. Inside the synchron motor operates opening the valve and at the end of its travel touching a micro switch to send a live feed to the pump.

things can go wrong in the valves synchron motor failure, micro switch stuck full on or off, ball in valve which closes opens ports can rot away. Or your system might not have one.

[meldrewreborn]

And the IHD gets its data from the meter which the supplier could update to get a better (though never exact) calorific conversion factor.
i find the overall value drifts only slightly and as other factors are fixed values I can work on the imperial conversion of measurement times 31.6 to give kWh. 11.2 for metric.

[geoffers]

Originally Posted by meldrewreborn

And the IHD gets its data from the meter which the supplier could update to get a better (though never exact) calorific conversion factor.
i find the overall value drifts only slightly and as other factors are fixed values I can work on the imperial conversion of measurement times 31.6 to give kWh. 11.2 for metric.

Just checked the CV actually stored on the meter, and it's near enough the same (39.5) as my bill (38.9), so the calculations actually shown on the meter (and thus displayed in the IHD) are spot on....

.... so I have to admit my early morning calculations on the earlier post must have been in error 🤓 (may have been to do with the ½hr lag between the GSME talking to the IHD, though I thought I'd left enough time for that to sort itself out)

[TAYLOROY]

@geoffers

this is really great info, I will definitely be trying this myself.

also thanks for the link to the device for switching as well.

[geoffers]

Originally Posted by JoeSoap

When I had this problem I realised that my boiler thermostat was set to a lower temperature than the hot water cylinder thermostat. That meant that the boiler could never satisfy the demand of the cylinder so the motorised valve to the tank coil stayed open and the pump kept running.

Once I set my tank thermostat to around 60-65 degrees and the boiler thermostat to around 80-85 degrees it cured the problem.

@TAYLOROY @meldrewreborn
I can confirm this was exactly the case - I set the boiler temperature up a tad and dropped the tank thermostat to 55⁰C. The system reached this after about ½ hour, with the pump and boiler turning off at this temperature.

So I upped the tank thermostat back up to 60⁰C and it ran for another ¼ hour before turning off. (This in fact makes for a perfect comparison since the electric immersion must have run for about 40 minutes to reach the tank temperature)

So this time the gas used was 0.406m³ x 11.2 = 4.55kWh @ 7.2p: Cost=32.7p

This compared to the electric immersion of 2.33kWh @ 9.5p: Cost 22.13p, so still about ⅔ cheaper using electricity than gas! (...on Next Drive ToU tariff)

This also clearly highlights the inefficiency of the gas boiler's indirect heating of the hot water tank via the heat exchanger, since "Ye canne change the laws of physics" which state that

1 litre of water takes 1 kilocalorie (4,184 Joules ) to raise the temperature by 1⁰C

So nearly half of the energy used ie. (4.55 - 2.33)=2.22kWh ==7,992 kilojoules of energy is being wasted by the indirect heating😯

This test also has identified an issue I hadn't been aware of by not having the boiler feed water temperature high enough the water didn't reach the tank thermostat temperature so the boiler/pump just kept running, which could potentially increase cost significantly!

[meldrewreborn]

@geoffers

Great analysis @geoffers.

On the issue of wasted gas, if the loss is to the outside then it is indeed a loss, if its lost inside in winter it just reduces the cost of home heating, so in my view neutral.

The best cost advantage might be gas heating of your hot water in winter and electric in summer.

[JoeSoap]

Originally Posted by geoffers

... This test also has identified an issue I hadn't been aware of by not having the boiler feed water temperature high enough the water didn't reach the tank thermostat temperature so the boiler/pump just kept running, which could potentially increase cost significantly!

I found this out when I had a new boiler installed several years ago. It has a thermostat dial that my old boiler never had so I turned it down in the summer. Then I noticed the pump was running... I took it upon myself to learn all about my CH/HW system and worked out what the problem was.

Glad it's sorted 👍

[geoffers]

Originally Posted by meldrewreborn

@geoffers

Great analysis @geoffers.

On the issue of wasted gas, if the loss is to the outside then it is indeed a loss, if its lost inside in winter it just reduces the cost of home heating, so in my view neutral.

The best cost advantage might be gas heating of your hot water in winter and electric in summer.

👍 Cheaper for me to use leccy all year for heating my water on the ND tariff 🤓

Interesting discussion of boiler efficiency here ... https://www.theheatinghub.co.uk/arti...fficiency-tips

However 70/80degC is too high for modern boilers to operate efficiently for heating.

For condensing boilers, a lower flow temperature is needed in order for the boiler to recycle heat that was previously lost through the flue. This has the potential to improve the boiler efficiency from around 78% efficient (non-condensing boilers) to 92-97% efficient for a condensing boiler.

In order to reach 92% efficiency however, the flow temperature for heating needs to 60degC or less, but this is too low to maintain a safe cylinder temperature.