Aero Indirect hot water tank and Viessmann boiler problem noise

ap · 05-25-2011, 05:30 AM

I also posted this on the Water Heater forum - sorry for the double post but perhaps this is more a boiler issue....

My Aero indirect hot water heater and/or my Viessman oil fired boiler isn't working and there is a rythmic "whoosing" noise cycling on and off coming from inside the Aero DHW tank. There is a Grundfos pump on the boiler hot water feed to the DHW tank just before the tank and it "feels" like it is operating. However ithe pump gets hot even though I cannot feel any heat in the hot water feed pipe from the boiler that goes into the pump - I suspect that the high heat is from the pump running dry or ??. BTW pushing a bleeder valve on another nearby hot water feed resulted in a good stream of water.

The boiler display has an indicator light which, according to the manual, says that it is being called for DHW BUT the boiler doesn't seem to want to fire up. I tried to reset the burner and using the override switch I got the boiler to fire for a while but it shut down after a minute or less even with the DHW light remained on.

I am not sure whether I have a faulty hot water tank, circulating pump or malfunction on the boiler... or all three!! any one have a similar experience or recommendation. Thanks

**jadnashua** · 05-25-2011, 12:08 PM

First, verify that the pump for the indirect is getting power. If it is, and the pipe to the indirect is not hot, if it isn't an air lock, the pump is bad (or you've got a valve closed that shouldn't be). My guess is that the boiler is timing out, sensing that the water temp is high, the return is not cooling it off, and shutting down because it doesn't make sense. After a reset period, it tries again.

Another thing to check is that the thermocouple for the indirect is fully seated in the well in the tank. But, since the water is not the proper temp, and it does call for the boiler to heat, it probably is okay. There are test procedures for the sensor, but you probably don't need to run them. They generally require a multimeter.

ap · 05-26-2011, 05:20 AM

Thanks very much for the suggestions .. I think you are right that something is shutting down the boiler and now I am inclined to believe I don't have a boiler "problem" but that something else not quite right. You are most likely right when you point out that their may be a blockage.....

I contacted Aero yesterday (now Bradford White) and the gentleman I spoke with was VERY considerate and certainly more helpful than ANY other manufacturer I have talked with as a consumer in recent years (good for Bradford White!!) and gave me a great deal of insight into the indirect heater. He suggested that there may be a block in the exchange plate that (if not cleaned on schedule) can get clogged with sediment. I am pretty confident that this has not been done - certainly not by me and I am suspicious that the previous owner did not either. I am going to look into this tomorrow.

I have scheduled a visit for furnace service anyway. The service man is expert on the boiler and the burner ... but I don't know what his level of expertise is with the balance of the plumbing. My furnace room looks a little like the control room on a Balao class sub.

Thanks again!!

ap · 05-30-2011, 12:16 PM

Well the Furnace repair man (s) arrived on the weekend. Apparently the little round pressure gauge mounted on the back of the boiler isn't supposed to be on "0"

...
I also learned what the valve was supposed to do on the cold water line that brings fresh water into the system. Once it was jiggled a bit - it brought the pressure up to about 15lbs.

This made the furnace happy ... but still no hot water. After the repair men left - having declared the burner fully functional... I removed the boiler feed and return lines from the indirect water tank and checked for blockages ... when I reconnected them and opened the feed and return valves...voila ... hot water began to flow into the exchanger plate and eventually all was well. I am learning!! A little slowly to be sure ... thanks again jadnashua

**jadnashua** · 05-30-2011, 04:25 PM

Double-check the manual on the boiler...most of them have some sort of display and error codes often can at least help you in the right direction. If the internal pressure was low, it should have said with an error message. Most boilers won't even try to fire if the water pressure is low. If you don't have an autofeed valve, then you need to monitor and add water. Now, since it is a closed system, you really shouldn't have to add water. Monitor it, and if it drops again fairly fast, you have a leak you must find. In theory, you could go years without adding any if everything is tight.