Hot water feeding into header tank

[gezmonder]

Hello, I have a standard gravity fed heating system in a four bedroom house. A couple of big rads in the extension which are downstairs in what is effectively a spur take quite a while to heat up. They do heat up fully but it takes a while compared to the others. I turn the pump up to position 3 and that helps quite a bit but when I do, an overflow pipe from the airing cupboard into the header tank runs pretty much constantly dropping very hot water into the header tank bringing the overflow into operation. So I have dropped it down to position 2 which isn't too bad but not ideal, I don't know if I should worry too much but I don't like the idea of running the pump at full whack all the time anyway, it doesn't feel like good practice. I'm wondering if it's up to the job and if the system has grown beyond the size of the pump since the extension.

BTW I am not a plumber, I have some rudimentary DIY knowledge.

 

[joni os]

Initial thoughts are extension rads are connected off extended 15mm pipework, If so get a plumber to correctly size pipework. Simple job if access to main flow and return available.
.

 

[gezmonder]

I would think it highly likely that they have been extended off of exiting 15mm pipework from where the old radiator upstairs used to live (now two larger ones), down to where the new ones are in almost directly below downstairs in the kitchen (two much larger ones). This happened a couple of years ago, I used the pump up to position 3 as a workaround and thought that was fine, until I noticed the hot water overrun a couple of months ago.

Please excuse my ignorance how should it have been done? Should it be using 22mm? I'm guessing you are suggesting that 15mm is causing too much resistance? These pipes are embedded in the walls and under the concrete floors now.

 

[joni os]

Water is the means of transporting heat from boiler to radiators. The flow of water/rate of heat transfer, is dependant on pipe size,pipe friction and pressure differential. A 15mm pipe can only transfer so much heat. BTUs to a group of radiators.
It is possible existing 22mm can be extended sufficiently without disturbing embedded pipework. Extensions often mean that existing radiators become redundant and much can be achieved by properly balancing system.
The fact that extension was done without proper consideration of heating indicates how advisable it is to engage a heating engineer at this stage to make the most of your current system.

 

[JackPlumber]

Hi. I have very similar problem. I have gravity system with solid fuel stove and oil boiler with dual coil cylinder. Everything worked fine until I replaced the oil boiler with an air to water heat pump. The new heat pump wasn't working great and was reaching 50Celsius very quickly with little heat output from rads. Turns out the HP has a large 400W circ pump. This was pushing a large flow up the vent pipe and into the header tank with 50C water in the header tank. I did a silly "fix" of bending the overflow pipe into the header tank to stop the splashing and noise from attic. Now the DHW from immersion is thermo looping from solid fuel coil in header tank. And cylinder is cold couple of hours after immersion is switched off.

My new idea is to bend overflow pipe back out of the header tank and fit a TP valve on end of it to stop overflow from high powered HP circ pump and still allow for pressure and temperature relief in event of solid fuel high output.

Anyone see any issues with this? I understand it prop doesn't meet any regulations but I am only interested in safety and practical working of the system. Any help/advice would be greatly appreciated