reversed water flow in radiant heating

eastar · January 2017

I have one room with floor radiant heating using hot water. The problem is even after I turned off the thermostat (which itself is brand new and works perfectly fine), the room still keeps heating up. The reason is the hot water goes out from the cold water inlet of the water tank, goes around the pipes and returns to the hot water outlet of the water heater , that is, the water flows in the reverse direction. I can stop the water flow by shutting off the manual valves of the cold water or the hot water, or both to the radiant heating. I suspect three things, 1) the valve (near the hot water outlet) normally controlled by the the thermostat is defective and hence constantly in an open position, 2) there is a systematic problem of the radiant heating installation – why it allows water to flow in the reverse direction?, 3) the hot water tanker is not working normally,i.e. why it allows hot water goes out from the inlet of the cold water?

Jamie Hall · January 2017

It's number 1. Neither the pipe nor the tank particularly care which way the water is flowing. There is nothing to prevent the water from flowing either way in the pipe, nor is there anything on the tank to prevent the water from going out the inlet.

hot_rod · January 2017

Is this a combination system with domestic after and heating water all the same?

eastar · January 2017

@hot rod , it is a combined system. The only hot water tank is used for everything in my home.
@Jamie Hall . Problem in number 1 must be there. Otherwise the water cannot flow without an opening/circulation. I can also confirm that there is no leak in the pipe because I can turn off valve in either end to stop the heating. But I am not sure my system is installed the correct way. It is "by design" to let hot water water flow from the hot water outlet, pass through a three way mix, then go to a water circulation pump(from Grundfos, installed in that direction), go through the pipes and then return from the cold water inlet. Even if I fix the valve, I am wandering the water may still flow in the wrong direction (then the circulation pump is counter-effective, why I need it?)
The water valve is controlled by a AG13A02A which is in turn controlled by the thermostat. Do you know how to determine that this is the problem of the actuator or the valve? I should be able to replace the actuator myself but changing the valve is too much for me. By the way, the actuator generates rattling noise when it is "working", indicating a problem there.

hot_rod · January 2017

sketch it out for us. some of those combined systems were piped that all water runs through the radiant whenever you flow water. the intention was "free" cooling in summer months. It could be it needs better control of the pump for just heat, not dhow recirc.

eastar · January 2017

@hot rod , thanks. I attached a PDF.

Jamie Hall · January 2017

I have to admit that I don't like systems which are piped to mix the domestic hot water and the heating loop. However...

If that zone valve is closing, you shouldn't get any flow in the heating loop. So that's the first place I'd look.

Now. That said. I recommend very strongly. In fact, I can't recommend too strongly. That you make absolutely sure that if the heating loop has not been used for more than two days -- such as might be in the summer -- you run the loop -- zone valve open and circulator on -- long enough to completely flush that piping every two days at a minimum, and bring the mixing valve up to at least 130 F and the hot water up to at least 130 F while you are doing it.

Gordy · January 2017

To the OP google legionella, and read up on it. That system should be separated with a heat exchanger so the dhw does not mix with the heating water.

Legionella bacteria needs 130 degrees min. to be eradicated.

hot_rod · January 2017

your drawing shows 1 pump, the pic shows two?

I suspect one is for DHW record? Runs all the time? if so.it is possibly inducing flow?

The pumps should all be bronze or stainless, they look to be cast iron?

It is not the preferred system of the plumbers here, mixing DHW and heating like that.

How much time and $$ do you want to invest. It should be able to function properly, but a heat exchanger isolation would be the preferred fix for bacteria concerns.

eastar · January 2017

Both pumps are Grundfos UP15-42F Circulator Pump. Yes they are cast iron. The one in the front of the picture drawing hot water toward the space heating inlet of the hot water tanker. I do not really know why we need it. Possible it draws some hot water to heat space around the hot water tanker itself? That is not needed though because the hot water tanker is in the basement and the basement is quite warm.

I just bought this house recently so I do not really know the systems. I am considering two options one is to fix this system (including a heat exchanger thank you for suggestion), the other option is to decommission this system. I am actually shutting it off now (by doing that I am risking in losing the system permanently - the pipe goes through the inside wall of the garage towards a separate room in the other side of the garage. The pipes might be frozen and eventually broken without hot water.

Gordy · January 2017

I would not do that. The system can be salvaged. We are warning of the risks by not correcting it.

hot_rod · January 2017

If you choose to repipe it correctly, completely drain down and maybe use compressed air to get any water out of the system, if freezing is a potential.

To correct the system a simple heat exchanger, and possibly reuse some of the components you have.

There use to be some manufacturers that offered HX packages for water heaters that were plug and play, I see if any are still around that build modules.

Solid_Fuel_Man · January 2017

Taco XPB would be an all in one HX and circulators with a controller. Designed exactly for this application.

reversed water flow in radiant heating

Comments

Categories