Has anyone had experience of this type of set up. I was wondering if "churning" the water in order to get a more even store temperature was successful. If so what type of pump was used.

Sadly, this one's in the middle

That's a good question. Is it a DHW tank or a CH tank or combined?

I would of thought that a cheap CH pump between the two 1/2" stat ports would fit the bill nicely. For controls I would start off by connecting it to the same circuit that switches on the central immersion heater 'cos it is when this has power is when you want to de-stratify.

Note - The stat ports on my TS are closed, that is they are just pockets and the stat sensors don't get wet. If yours are the same then you will have to run a drill through them

Do you have a laddomat or similar loading system for the biomass boiler? This could be used in a couple of ways

1) connect an external electric heater in series with the boiler, use that the same as you do with the boiler so the laddomat heats the whole tank volume while maintaining stratification . Then the hot tap still runs hot even when the tank is nearly "empty" of heat.

2) use the pump in the laddomat to pump cold water from the base of the tank round through the boiler and return to the top, where it will sink past the internal immersions and be heated. This might need a mod to the laddomat thermostat plunger, sure I saw instructions for this online somewhere.


If you do connect a new pump then no need to use the stat ports, just tee into the cold water feed pipe and the hot water outlet pipe, near to their respective connectors to the tank.


FWIW the Mixergy hi-tech tanks use their external PHE pump to destratify when connected to a heat pump, so the HP 'sees' a colder flow and runs more efficiently. Not relevant for an immersion tho.

Posted By: owlmanDownside is having to drain the tank which has inhibitor in it.

I've seen an immersion heater in the bottom of a tank changed 'hot' that is without draining the tank. The vent was blocked up (the only place that air could get in) and then the immersion heater was unscrewed and the new one put in - quickly. I was surprised at how little water came out, a couple of blubs and that was it, nothing that could not be managed with a towel. In your situation you could make a fitting to replace the plug e.g a male threaded piece of pipe to replace the plug with a tap on the end - turned off -, put sealant on the fitting then remove the plug and quickly replace with the fitting.once done you can put what ever you want on the outboard end of the tap. (ditto the top connection) If you get it wrong then the you will get drips which may need a drain down but you were going to do that anyway. (you are a brave man if the TS is upstairs with a carpeted landing and stairs)

Posted By: owlmanI still can't figure out though what would be best regarding pump flow direction. Hot top to cold bottom, or cold to hot. That's where the whole plan may go awry. I also have to consider pump types especially impeller material in view of potential high temperatures, plus as I mentioned flow rates.

If you use a standard cheapo CH pump with the usual 3 speeds then you can experiment with flow rates and for direction - well the CH pumps have ball valves each end to facilitate changing so you can turn the pump around easily. Flow rates can also be varied by throttling the ball valve on the pump. CH pumps will also stand heat up to the old fashioned CH flow rate temps of about 80 deg. Its probably easier to experiment than to try and calculate or over think the project.

It was a 1 1/2" thread 3kW immersion heater that went in horizontally at the bottom of the cylinder.
https://heilmann.hu/spd/3033-14/Heizer-Hajdu-bojler-STA-kompakt-futobetet-6-4-3000?utm_source=olcsobbat&utm_medium=shopping&utm_campaign=olcsobbat_shopping_heilmann_haztartasi_gep_alkatresz&utm_source=olcsobbat&utm_medium=shopping&utm_campaign=olcsobbat_shopping_heilmann_haztartasi_gep_alkatresz&gad_source=1

Pipe threads here are quoted in multiples of 1/4" so 1 1/2" = 6/4"

So yes a bit smaller than what I remember going into the top of a copper cylinder in the UK

@ PiH The risk taker in me would love to have a go at the full tank method you describe and I can understand the principle. However, I have visions of me with a finger in the hole reaching for the spanner I've dropped, I shudder to think. On the plus side it's all on the ground floor in the integrated garage with drainage to hand.

@ WiA Thanks, yes, hot to cold is what I'd instinctively go for, your calcs. broadly reflect what happens in practice.


I'd looked at a couple of low flow circulating pumps that only move about 1/2 Cu M per hour, this type of thing:-

https://www.mrcentralheating.co.uk/dab-vortex-bwo155-r-zm-blueone-1-2-domestic-hot-water-pump

https://www.anchorpumps.com/pump-type/hot-water-service-circulators/grundfos-comfort-hot-water-service-circulators-240v

There are others of this albeit expensive ilk. I think they were mainly designed for re-circulating DHW systems hence the low flow rates.

@ WiA At the moment with 2 x 3kW immersions for 7 hours I'm heating about ( Very rough guess here, difficult to get a true figure ), 900L from a 50C start, to 80C. My aim, with the addition of another 2 x 3 kW immersions and a circulator, would be to raise that 900 L to about 15/1600 L.
Worst case doing that each night on cheap rate would be 12 kWh for 7hrs @ 6.7p would be £5.63 per night .I think, it would be a lot less than that as often we don't use that much for the zoned CH. Also because the 4 x 3 kW immersions are wired independently on 4 timers I could mix and match the input according to demand.

I think for the methodology to work you would to have the malleable iron fittings made up beforehand with a lever type ball valve in order to fit the copper afterwards, as you suggest. Maybe with taper fit rather than straight fit too.
Buckets at the ready

Posted By: Cliff PopeI thought the principle of an "ideal" tank is that it is heated at the bottom and the hot water rises to the top.

This thread isn't discussing an ideal tank, but the realities of owlman's tank.

Hi Will, Thanks for the formula, yes i was aware if the load implications and independent breakers and timers is what we have.
The first 2 x 3 kW didn't have stats on them because with such a large water volume There was no chance of overheating and the system is well protected with pressure relief valves. However if I do go for another 2 x 3 kW those will have inbuilt stats, for flexibility as well as safety.
When we fitted the storage batteries we split the tails and took off a separate feed just after the meter via a double pole fused isolator. this is the dedicated immersion feed. We also wanted to eliminate any risk of the immersions draining the storage batteries, and it was easier to monitor that way.