A new problem...

Ronanmd1

Hey guys. I have a Weil-McLean cast iron boiler supplying the in-floor heat to my basement slab, and garage, and in-floor heat to several bathrooms in my home. The house also has a natural gas furnace and a separate hot water tank.

My mixing valve recently sprung a slow leak. Our boiler company replaced the mixing valve and topped up the glycol in the reservoir tank. At the time, he mentioned that he could not seem to get the pump in the reservoir to kick on, so used water from our hot water tank to fill the system back up. For the past few weeks, everything has been going well. I have been keeping a close eye on the supply/return temps and the reservoir level and all have been as expected (including this morning)... Until about an hour ago I heard a weird rumbling noise from the mechanical room. The noise was coming from the reservoir pump. The glycol is nearly empty in the reservoir and the pump was still running. I immediately shut off the boiler system.

Now, despite the low volume in the reservoir tank, the pressure on its gauge reads 30 PSI. The pressure valve on the expansion tank also reads above 30 PSI (off the top of the gauge on the scale). The pressure reading on the boiler itself is also higher than the warning mark on the gauge.

At first, I thought I had sprung a leak in one of my zones, but I can't find any evidence of a leak in the house. Also, I would think that the pressure in the expansion and reservoir tanks would drop (not rise) if there was a leak in the system. Unless the pump filled it with air while it was running?

Since the pressure in the system seems high and the pump in the reservoir was obviously trying to fill the system (and since my plumber had trouble getting the reservoir pump to work as he expected when he was trying to fill the system), is it possible that the problem is with the reservoir pump itself and the pressures are high because it was adding glycol to the system when it wasn't needed, and wouldn't shut off, thereby increasing pressure in the system?

Thanks for any suggestions...

Jason

Jamie Hall

How big an expansion tank is on the system? And how much glycol seems to have been added?

Is the glycol also an expansion type tank -- that is, is there an air cushion in it? If so, to what pressure is it normally pressurised?

Ronanmd1

Hi Jamie - The tank is new from a year ago. It is a Calefactio HGT-60. It has an air bladder. Its capacity is 8 US gallons. The label says the precharge pressure should be 12 PSI. Max allowable pressure is 30PSI. I think it normally was reading 15 PSI. The glycol was filled to the 'max' level on the reservoir where it remained stable until today.

Jamie Hall

Something just doesn't compute here. If the glycol tank has emptied itself -- or nearly so -- and it has an air bladder, its pressure should have gone down. On the other hand, if it doesn't have an air bladder, its pressure is not relevant. That is what has me puzzled.

If the glycol feed pump went bananas, yes it could possibly raise the pressure of the rest of the system -- but as I say not while keeping the pressure in the glycol tank high.

Can we have a sketch of the system?

EBEBRATT-Ed

@Ronanmd1

Yes. It sounds like the pressure switch on the glycol MU tank is NG and that it filled the system when not needed. I would drain the Glycol out of the boiler until you back to 12-15 psi.

Then get the glycol pump/switch fixed

Ronanmd1

Thanks guys. That was what my amateur brain was thinking as well. It seems too coincidental that the tech couldn't get the pump to work properly (in his opinion - but with limited experience with that particular brand of tank/pump) when he was trying to fill my system back up after replacing the mixing valve. Will call them in the am to have them come look at the system again and drain it back down. Will also advise them to bring a replacement tank/pump with the presumption that it is the issue. Thanks again for all the advice. Much appreciated.

hot_rod

Some fill tanks have pressure reducing valves that are set to desired fill. See if yours has one, and maybe he cranked it up to fast fill.

Does the relief valve go into the tank or bucket so you don’t lose a bunch of glycol if the relief pops?

pecmsg

I have to ask

You are using Premixed glycol?