Aqua Hot front zone not heating

[Dr4Film]

After looking at the service manual for the 600D model, your check valves appear to be located BEFORE the pump mounted to the side of the Aqua-Hot near the tank. Whereas the check valves in my 431/12 model are after the pump and sit high above the case.

If you remove the hose end off the input side of the pump I would think that should tell you if the check valve is blocked with no fluid running out.

To replace any check valve in the 600D, you have to drain the coolant from the boiler tank.

is it possible to take the top of the check valve apart?

[dandick66]

I have the 400D model, so it only has 2 pumps and 4 zones.  Pump 1 controls zone 1 and pump 2 controls zones 2,3, and 4 and is the circ pump for hot water.   My front vents were blowing cool intermittently, or so I thought.  I checked everything and could not find anything wrong. I changed the check valves and the fluid, too.  What I finally found was that the wiring to the pumps from the AH control board were reversed.  As long as all zones were demanding heat via the thermostat it worked fine.  However, when zones 2-4 were satisfied and zone 1 demanded heat, the “wrong” pump would come on, but the “right” fans would come on.  It’s a little difficult to explain, but just double check your wiring.

Dan D, 2012 Diplomat 43DFT

[Pduggs]

1 hour ago, Dr4Film said:

After looking at the service manual for the 600D model, your check valves appear to be located BEFORE the pump mounted to the side of the Aqua-Hot near the tank. Whereas the check valves in my 431/12 model are after the pump and sit high above the case.

If you remove the hose end off the input side of the pump I would think that should tell you if the check valve is blocked with no fluid running out.

To replace any check valve in the 600D, you have to drain the coolant from the boiler tank.

is it possible to take the top of the check valve apart?

I think my AH might have a different arrangement. Here’s a picture of it. 

[David Pratt]

It is not uncommon that at times the Heat Exchanger can get Vapor Locked. When this happens it acts like blocked hose or failed check valve. The circulation pumps are magnetic driven pumps, not direct drive pumps and are very low pressure flow/volume pumps, not pressure pumps. When a Heat Exchanger gets Vapor locked it will not clear itself because there is not enough pressure from the pump to do so.

Look at the check valve and you should see a small 1/4" bolt. This bolt is actually there to help bleed air from the system. With the pump operating slightly open this bolt until you get coolant flow and close it. If you still do not get any heat from the hose to the Heat Exchanger, then you will have to bleed the air out of the Heat Exchanger. THIS IS WHERE IT CAN GET MESSY. To bleed the Heat Exchanger you will have to Loosen/Remove the return hose on the back of the Heat Exchanger and install a short extension hose on the outlet and put the other end in a bucket. Turn on the pump until you get the air out and coolant is flowing into the bucket. Turn the pump off and Re-install the return hose and you should be good to go.

Heat Exchangers that have a hose nipple on the back across from each other, the left nipple looking from the front of the Heat Exchangert in most installations, should be the inlet and the right one is the output. If the nipples are mounted to just one side, the top nipple is the inlet and the bottom nipple is the output.

[Pduggs]

52 minutes ago, David Pratt said:

It is not uncommon that at times the Heat Exchanger can get Vapor Locked. When this happens it acts like blocked hose or failed check valve. The circulation pumps are magnetic driven pumps, not direct drive pumps and are very low pressure flow/volume pumps, not pressure pumps. When a Heat Exchanger gets Vapor locked it will not clear itself because there is not enough pressure from the pump to do so.

Look at the check valve and you should see a small 1/4" bolt. This bolt is actually there to help bleed air from the system. With the pump operating slightly open this bolt until you get coolant flow and close it. If you still do not get any heat from the hose to the Heat Exchanger, then you will have to bleed the air out of the Heat Exchanger. THIS IS WHERE IT CAN GET MESSY. To bleed the Heat Exchanger you will have to Loosen/Remove the return hose on the back of the Heat Exchanger and install a short extension hose on the outlet and put the other end in a bucket. Turn on the pump until you get the air out and coolant is flowing into the bucket. Turn the pump off and Re-install the return hose and you should be good to go.

Heat Exchangers that have a hose nipple on the back across from each other, the left nipple looking from the front of the Heat Exchangert in most installations, should be the inlet and the right one is the output. If the nipples are mounted to just one side, the top nipple is the inlet and the bottom nipple is the output.

Thanks. I’ll give that a try. 

[Dr4Film]

1 hour ago, Pduggs said:

I think my AH might have a different arrangement.

Yes, it certainly IS different than the 600D Model that Aqua-Hot has in their library for the Service Manual. I guess someone at the factory thought that placing the check valves before the pump was a bad idea but forgot to change the manuals.

[Pduggs]

3 hours ago, David Pratt said:

It is not uncommon that at times the Heat Exchanger can get Vapor Locked. When this happens it acts like blocked hose or failed check valve. The circulation pumps are magnetic driven pumps, not direct drive pumps and are very low pressure flow/volume pumps, not pressure pumps. When a Heat Exchanger gets Vapor locked it will not clear itself because there is not enough pressure from the pump to do so.

Look at the check valve and you should see a small 1/4" bolt. This bolt is actually there to help bleed air from the system. With the pump operating slightly open this bolt until you get coolant flow and close it. If you still do not get any heat from the hose to the Heat Exchanger, then you will have to bleed the air out of the Heat Exchanger. THIS IS WHERE IT CAN GET MESSY. To bleed the Heat Exchanger you will have to Loosen/Remove the return hose on the back of the Heat Exchanger and install a short extension hose on the outlet and put the other end in a bucket. Turn on the pump until you get the air out and coolant is flowing into the bucket. Turn the pump off and Re-install the return hose and you should be good to go.

Heat Exchangers that have a hose nipple on the back across from each other, the left nipple looking from the front of the Heat Exchangert in most installations, should be the inlet and the right one is the output. If the nipples are mounted to just one side, the top nipple is the inlet and the bottom nipple is the output.

I checked for the nipples you speak off on the backside of my heat exchanger. See pictures. They don’t appear to be on mine. I’ll bleed the check valve and if that doesn’t work I’ll bleed the return hose at the heat exchanger. Do you know which hose is the return?

[David Pratt]

The nipples are the ones that the hoses are connected to on the rear of the heat exchangers.

Heat Exchangers that have a hose nipple on the back across from each other, the left nipple looking from the front of the Heat Exchangert in most installations, should be the inlet and the right one is the output. The one hose connection shown in the second picture should be the return hose if it was properly plumbed from the factory.

[Pduggs]

Thanks so much!

[96 EVO]

Assuming one or more of your heat exchangers on that zone are in a slide, you may need to get your eye's on the feed / return line, and look for kinks.

Have you tried this zone with both, slides out and in?

Edited October 1, 2021 by 96 EVO

[Chargerman]

Did you recently change the boiler fluid?

you could also try filling the line with fluid at the heat exchanger 

Edited October 1, 2021 by Chargerman

[Pduggs]

I don’t think I’ve tried it with the slides in. 
 

I haven’t changed the fluid. Likely original fluid with some added over time. It’s dark in color. I believe I read Aqua-Hot doesn’t recommend replacing the fluid unless it’s contaminated or lost it’s effectiveness. I did check it with a 3-1 refractometer and it was within spec. 

[Chargerman]

Ok. I was just curious if the fluid was recently changed as it would be cause for air in the system. Would be a bit surprised to see air in your system if nothing was changed out and/or your fluid never got low. 

[Pduggs]

To follow up, I decided to replace two of the old pumps with the new Behler pump. I have four pumps. One is for engine pre-heat. The front two zones I replaced. I now have plenty of heat throughout the coach. After installing the new pumps, I ran the system for a day or so. I could see air bubbles in the lines, but they worked themselves out after a few hours of operation. 
 

I had to remove all four pumps to get enough room to replace the two old pumps in the back, with the Behler pumps. That meant pinching off the all the intact lines. I probably lost a half gallon of fluid during this process. Since the Behler pump has larger diameter hose connections, you have to use a reducer. This makes things difficult because the back two pumps have very short intact hose lengths, but I managed to arrange the pumps to make it work. 
 

If you do this job, take lots of pics as you go. Make sure you match up the correct electrical connections to each pump. I used all new hose clamps and gladly threw away those worthless wire clamps AH used, that are nearly impossible to remove. I checked all four check valves to see if they opened and closed freely, and they did. So, no need to replace them. 
 

The job took me about four hours to complete, while sitting on the ground. I had a hard time getting up after all that. I recommend getting up and moving around every so often.

Edited October 27, 2021 by Pduggs