Issues with using an indirect water heater as a buffer storage tank

VanUnamed

Hello all!.

So i have upgraded my heating system (coal fired boiler i built, big scotch boiler thing, with 150l tank), but now im facing circulation issues.

The boiler i had before was simply a very long pipe in which water was forced end to end.

the tank is an UK SANTON indirect unvented cylinder, PP210 model santon premier *210L)

the system goes like this:

boiler (hot side) ---> indirect water heater tank bottom port (where cold water used to go) ---> top exist of this tank ---> radiator loop ---> pump ---> boiler (cold side)

Issue is, i had extremely slow circulation, having the outdoor tank go easily to 60c, but the indoor tank remaining 30-40C behind even after 2 hours.

Today as an experiment i isolated this tank away from the system and just ran  outdoor boiler ---> radiators, it worked just fine.

After extensive chat with mr. chatgpt, it pointed out that  I have plumbed the tank like I did the radiators.  hot water in from bottom, cold water out from the top.

but water heaters (or storage tanks) aren't radiators, so the correct order would've been hot water in from the top, whereas the pump should draw the coldest water from the BOTTOM, of the tank. basically i was fighting convection.

What's your thought?

I am no sure if this was the right forum to ask, if i made a mistake i apologise

Thanks in advance for any help

hot_rod

With any tank that is being heated, if the pump is not running, no circulation then the tank will stratify

Hot water rises, cooler water at the bottom

you want cooler, bottom connection temperature going to boiler, the top high part of the tank goes to the radiators

Tall vertical tanks will show more stratification than horizontal type tanks

If either the boiler or radiator pump runs all the time, the tank will be mixed fairly well all the time

It depends somewhat on where the connections are into the tank

Tall vertical tanks sometimes have mid point connections

We would need to see a piping diagram and more info on how the system is controlled