Tankless in floor heating intermittently working..

phemor

Evening all, I'll try to be as thorough as possible..

Issue - I have a Rinnai tankless heating solution for in-floor tiled kitchen and the garage floors, it is intermittently turning on when called for by the thermostats.


The system




It's a Rinnai v53i. The left loop is the kitchen floor and the right loop is the garage floor. There is a thermostat in the kitchen and in the garage.
Cold water line comes into Taco 329-3 pressure reducing valve
Past a Extrol model no 15 expansion tank
Then through a water pressure gauge (currently at 40psi) before entering the Rinnai v53i.

After the Rinnai there is a 75psi relief valve
Followed by a Taco 00R-MSF1-41FC multi-speed cartridge circulator
Flows down to both loops, going through a motorized valve on the left side (honeywell model no V8043F1036) and a motorized valve on the right side, i can't make out the model no of this one.
Then it's off into the floors and back through.


The electrical side of things..

The main power comes up into the emergency shut off switch - Into a 2 x 2 wall socket boxes, one with a 'winter watchmen' light thing - Into something I've no idea what it is, I assuming some kind of relay?


From that into a Taco SR 501 zone switching relay.
The power from the sr501 goes into the Taco 329-3 pressure reducing valve.

The thermostat from the kitchen goes into the left motorized valve
The out of that valve goes into the right motorized valve along with the garage thermostat which goes into the right motorized valve too.
Then the output of the right one goes into the zone switching relay and the box to the left of it.

That's the entire system - The motorized valves are working, i can feel and hear them open/close then i turn the thermostats on/off. The zone switching relay lights up red but then the circulator doesn't kick on and thus the Rinnai doesn't kick on.

When it does decide to work, once the circulator kicks on, the Rinnai follows suit and it all fires up. I'm thinking the zone switching relay is biting the bullet but maybe it's something else? What methods can i test with?

Thanks,
Allan

neilc

cuz you're trying to use a water heater to do a boiler's job,
wrong application,

Jamie Hall

I resume this is a recirculating system?

If the zone valves open, does the pump kick on? You may not have enough flow to reliably turn on the water heater. There is a tremendous head loss through such a thing and the pump flow rate at that head loss may be just barely on the margin of what turns on the water heater.

Ironman

Though it may look similar to a wall hung boiler, it’s definitely not the same. The tankless is not designed for space heating: its heat exchanger has way too much resistance to flow. It’s designed to have house water pressure (60 psi) going into it and an open faucet on the other end. The hydronic circulator can only produce about a 5 psi differential.

People keep trying to use tankless water heaters because they’re cheaper than boilers. They’re neither designed, controlled or approved for space heating.

Every boiler manufacturer either could or does make tankless heaters. If a tankless could replace a boiler, there’d be no need to make boilers.

phemor

neilc said:

cuz you're trying to use a water heater to do a boiler's job,
wrong application,

Thanks for the useful response. I didn't do anything, this system was already installed in the house and functioned just fine for the last 6 years. If you have nothing constructive or helpful to say, don't.

GroundUp

I'm not going to beat the dead horse that is the tankless/boiler debate, though it is accurate. This appears to be upward of 10 years old and obviously has been working, so we'll leave it at that for now.

Open up the SR501 and put a meter on the circulator output terminal (usually #4 N/O). If it's getting 120v during heat call, the relay is doing its job. If the pump is not spinning, then the motor is on its way out. If that terminal does not have power during heat call, then the relay is failing.

phemor

Jamie Hall said:

I resume this is a recirculating system?

If the zone valves open, does the pump kick on? You may not have enough flow to reliably turn on the water heater. There is a tremendous head loss through such a thing and the pump flow rate at that head loss may be just barely on the margin of what turns on the water heater.

Thanks for the response - I can certainly try increasing the pressure behind the system via the reducing valve. The system has run consistently with lower pressure than is currently being read on the display. I believe the Rinnai minimum is 20psi, although recommended 30-80psi and my gauge is currently sat at 45psi.

phemor

GroundUp said:

I'm not going to beat the dead horse that is the tankless/boiler debate, though it is accurate. This appears to be upward of 10 years old and obviously has been working, so we'll leave it at that for now.

Open up the SR501 and put a meter on the circulator output terminal (usually #4 N/O). If it's getting 120v during heat call, the relay is doing its job. If the pump is not spinning, then the motor is on its way out. If that terminal does not have power during heat call, then the relay is failing.

Thank you, I appreciate this. I'll give that a shot.

neilc

phemor said:

don't.

but I did

neilc

actually,
here's an idea,
check and clean the strainer screen

Jamie Hall

Friend, you haven't answered a critical question which I asked. Is this an open system or is it closed? If it's a closed system the pressure on your gauge is quite irrelevant to the problem.

If it has worked in the past, and doesn't now, there really are only two alternatives: the filter screen in the water heater has gotten clogged, increasing the head loss through the water heater to the point where the pump can't create enough flow to trip the water heater's flow switch, or the pump itself isn't generating enough flow.

I sincerely hope there is a standard water heater temperature and pressure relief valve on the system at the water heater. I don't see one, but maybe there is?

phemor

Jamie Hall said:

Friend, you haven't answered a critical question which I asked. Is this an open system or is it closed? If it's a closed system the pressure on your gauge is quite irrelevant to the problem.

If it has worked in the past, and doesn't now, there really are only two alternatives: the filter screen in the water heater has gotten clogged, increasing the head loss through the water heater to the point where the pump can't create enough flow to trip the water heater's flow switch, or the pump itself isn't generating enough flow.

I sincerely hope there is a standard water heater temperature and pressure relief valve on the system at the water heater. I don't see one, but maybe there is?

Apologies I missed that before. There is a 75psi relief valve on the left side of the hot isolation valve.

The water in the loop is recirculated, it comes out of the radiant floor and pipes back in to meet the cold supply which i guess is just to top up the system as needed. I'm unsure if that counts as closed or not?

Hopefully this helps


I'll check the filter screen and the electrical suggestion earlier for the zone switch

EdTheHeaterMan

To understand the pressure issue and why it is irrelevant: On an open system (what the appliance was designed for) the inlet or cold water side will have 60 PSI from the home's cold water supply. The outlet will have the same pressure when all the hot faucets are closed. When a faucet is opened the outlet side will have zero pressure on it at the open valve. That means that there is 60 PSI forcing water through the heat exchanger.


ON YOUR SYSTEM the inlet water pressure is the same as the outlet pressure when the circulator pump is off. When the circulator pump is on, the pressure difference of a circulator pump is less than 8 PSI in most cases. That means that the water flow across the switch that turns on the burner is operating very close to the minimum flow required. If there is any restriction added to that flow, then the switch will not activate the burner. The fact that it worked for 6 years does not make it the correct application for the job at hand. It means that someone got it to work "good enough for now". Well Now is over and in the past. So you may be looking at little things going wrong as the system grows older. It may come time when this will not be cost effective to keep repairing it. You may want to consider budgeting for a proper replacement in the next few years.


Please don't be offended by the comments about your appliance being applied to the wrong use. We see too many of these cases over and over. You obviously did not make the mistake, but you need to live with it.


Understanding how it is supposed to work and how it IS working "As Built", will be helpful in determining what is the best way to get it back working.


Another design feature of your water heater is that it is designed to take 50° to 60° cold water and heat it to 120° instantly, so you can take a shower. Your application is using the return water from the radiant heat which may be as warm as 90°, and make 110° water for the floor heat. That is another condition where the sensors on the heater may think there is a problem. On some models that 90° inlet temperature would cause the burner to stop operating.


Hope the strainer is your only problem and you don't need to get a new pump. If you do, you may need to get one that will have higher Head Pressure capabilities to increase the flow past the flow switch. But that may cause noisy operation due to the increase in the velocity of the water in the tubing. So many things to think about. Best of luck with your system.

Yours Truly,
Special Ed.