Help me fix my Viessmann Vitodens mess?

ada454

Hi! Please help a dumb guy clean up someone else's mess (that I probably made worse).

We bought a 5-year-old apartment with a Veissmann Vitodens 111-W B1LD-26 combi boiler. Below it is a separate Wilo DHW circulating pump.

Mistake 1: It's been 4 years since its last service. Oops.

Mistake 2: Our first time leaving for a week, I switched off the boiler using its power switch. This did not turn off the external pump, which was left to constantly circulate no-longer-hot DHW, 12 hours a day.

Soon our neighbour called to tell us a very loud "alarm" was going off inside our apartment. It turned out to be a VERY loud screaming/whistling noise coming from the boiler. Shutting off the external pump stopped the noise.

Mistake 3: Obviously I really should have got the boiler checked right then… I did not, since it seemed to be fine. (I also told myself good help is hard to find here in Croatia, which is an understatement.)

This weekend I filled the boiler to 1.2 bar. Within a few minutes it was slowly dripping water. I slid off the cover and found the automatic air vent leaking from its clearly cracked top. I also found a telltale paper towel that says I'm not the first person to discover this leak.

I've got a heating company coming to take a look, but given my mixed repair experiences here in Croatia, I want to arm myself with more knowledge than I have right now.

1. Any guesses on the loud noise? I know the external pump was pointlessly circulating water, but I don't know enough to understand how/why this affected the boiler, or if this could have caused (or been caused by) the physically damaged AAV.
2. When the heating engineer comes, is there anything else I should insist on having done? A flush, maybe?
3. The external pump is connected directly to the boiler's mains input, so the circuit breaker is currently the only way to shut it off. That seems bad, right? Given it's just a little 6-watt pump, could I move it to the empty switched circuit that's meant to power a 230 V thermostat, or is that a terrible idea?

Thanks for any help you can offer! I'll see if I can figure out how to add a picture or two.

ada454

Cracked vent cap.

I don't think that paper towel is OEM.

mattmia2

Automatic vents eventually fail and leak. The cap should be loose on it to allow it to vent. Tightening the cap will seal it off if the cap isn't broken.

Is the circulator moving domestic heating water, water for space heating, or domestic hot water, potable water for bathing and washing and such? As long as the circulator had water and could move it, wasn't deadheaded on a valve, it should be fine running 24/7.

Alan (California Radiant) Forbes

The leaking air vent probably allowed enough water out for the pump to run dry and squeal.
The fill valve should have kept the system topped up, but they very often fail closed.
Replace the air vent and fill valve and see if the pump runs quietly once rid of air. If not, replace the pump.
Also, there should be an on-off switch on the boiler plus an electrical disconnect to cut power to anything associated with the boiler.
Hydronic systems typically don’t need a flush unless you use glycol. I would have them open up the combustion chamber and clean it of any coffee grounds and wash it down with water to make sure the condensate drains well. A familiarity with Viessmann boilers is not essential, but recommended.

EDIT: You say the external pump is for DHW. If so, my comment above is not valid since the external pump should be able to run forever even though the water is cold.

ada454

Thank you both!

Yes, it's a domestic hot water pump, I think it keeps hot water available at the taps. It's set to run when the return temperature falls below 40 ºC, so I know with the boiler off it would have run continuously, but I still have no idea why that created a problem. My only guess was it somehow created a pressure differential the boiler couldn't handle, but I don't know how or why. I was at least smart enough not to try reproducing the problem only to end up with a much bigger one!

The boiler's manual shows an external detachable filling loop, but I seem to have a manually operated integral loop that I'm guessing was optional.

The technician is here now to replace the AAV, after which I'll refill the system and we'll see if there are any other problems!

ada454

Thankfully the repair went well and we're now running at 1.3 bar. They'll come back next month for a standard service.

That vent cap was really cracked! I can't imagine boiler pressure doing that kind of damage; I wonder if the previous owner closed it so tight that it broke. (The new cap is properly loosened.)

I doubt I'll ever solve the mystery of why pump on + boiler off = extremely loud whistling from the boiler. Thankfully there don't seem to be any lasting effects now, and we'll just take better care of it going forward.

I am going to steal 6 watts from the 230 V thermostat circuit for the external pump, so it will turn off with the combi boiler's power switch. That's no more power than a smart thermostat would use, so it should be fine.

Thanks again for the help, and hopefully this information helps someone in the future.

ada454

FYI if you're coming here from Google: this is the integral filling loop on a Veissmann Vitodens 111-W B1LD-26. The manual doesn't mention this anywhere, yet there it is:

After you use it, that backflow preventer in the middle is going to drip for several minutes, and then you'll want to re-tighten the valves.