A
arkay-eff
Our building has a boiler that provides both hydronic heat and domestic hot water. It's been working without any serious problems for 10+ years. The DHW is heated via a coil and goes through a Holby mixing valve, which a few months back had a problem with the mix exceeding the maximum safe levels. The plumber replaced the piston mechanism, adjusted the temp and yet it continued to have the same problem: the water gets unsafely hot after a while and then eventually drops back to where it ought to be. They replaced the piston twice, the second time installing a low-temperature piston so that the highest it can mix is 130F (54C). Most of the time the temperature is fine, but when running a good flow of water, what I see is that eventually the mixed temperature drops to 105F (40C), it stays for for a minute or two and returns to the normal temperature. Lest you think that the coils aren't providing enough hot water, the entire time this is running the coil output thermometer shows the hot water going into the mixing valve is at least 160F (71C). That's the minimum it ever shows.
The other day I was testing this again and in fact the hot water stopped coming out of the sink briefly (!) and I reached for the handle and it resumed flowing. I have never seen anything like this happen or had any prior indication of a flow problem.
So here is the question: the plumber is convinced that the problem is not in the mixing valve. I have started wondering if there's something that could cause intermittent partial blockage in the flow through coil or into the mixing valve. We've had some street repairs on a broken water main in the past few months and a tiny piece of asphalt showed up in an apartment's filter. Is there something else we might be overlooking that could account for the mixing valve producing cold temps when there is a very hot water supply available?
The other day I was testing this again and in fact the hot water stopped coming out of the sink briefly (!) and I reached for the handle and it resumed flowing. I have never seen anything like this happen or had any prior indication of a flow problem.
So here is the question: the plumber is convinced that the problem is not in the mixing valve. I have started wondering if there's something that could cause intermittent partial blockage in the flow through coil or into the mixing valve. We've had some street repairs on a broken water main in the past few months and a tiny piece of asphalt showed up in an apartment's filter. Is there something else we might be overlooking that could account for the mixing valve producing cold temps when there is a very hot water supply available?
