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Old 01-24-2016, 11:32 AM   #1
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Shower exhibiting anti-scald behavior but can't find the valve?!


Hello. First time poster but longtime lurker here. I'm trying to finally address a problem that has been part of our home since we moved in 18 months ago. The house is small, from the early 50's, and is essentially un-updated since then, though very well maintained. Our domestic hot water is from a tankless coil integrated into the oil-fired boiler for the hot water heating system.

There are two related issues here:

1. Our domestic hot water at the kitchen and bathroom sinks is ridiculously, dangerously hot. There is a manual (non-temp-sensing) mixing valve at the domestic water outlet from the boiler which is seized, presumably in the very-very-hot position. This is a straightforward repair, just need to sweat it out and plumb in something better. I plan to upgrade to a whole house temp-sensitive anti-scald valve, BUT

... the thing I can not understand:

2. Sometimes the tub/shower will cut off nearly ALL the hot water... like it will wither away to something around room temperature, not immediately but as if you had run out of hot water in a conventional water heater. It does not seem related to the volume of hot water that's been used--sometimes we can't even draw a plastic tub of bath water for the baby without it getting cold on us. However, when this happens, the adjacent bathroom sink will still produce scalding hot water. I figured there must be a malfunctioning anti-scald valve built into the wall (this is an old old two handle system) but upon opening the back of the wall, there is nothing of the sort. The basement is unfinished and I can trace the water pipes from the boiler to the bathroom, and there is nothing but straight pipe and T's down there, no mixing valves or anything like that. This problem does not seem to happen when its warm out (summer), and may happen less in the middle of the day (when the boiler is only maintaining the low limit b/c the t-stat is calling for nothing). It is also intermittent... sometimes I can have a really nice shower. Note that the shower/tub NEVER produce the scalding temps that come out of the sinks. I believe this hardware is original to the home.

Wider shot of back of tub handles (that's the cold tap you see top left)


Close up of the T that connects mixed water to tub spout or up to shower...



I don't like to work on things I don't understand, so I'm reluctant to address the first problem without understanding the second... I do not wish to replace the shower controls at this time, just to either remove or replace whatever is limiting the hot water. But I can't find it. Would love some guidance.

Thanks.

Luke in NY
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Old 01-24-2016, 12:05 PM   #2
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Your tub valve does not look like an anti scald type. It looks like a two handle old fashion valve. Your boiler out to the house needs an automatic ASSE 1017 tempering valve. That you can set to desired temperature for the house hot water.
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Old 01-24-2016, 12:37 PM   #3
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change the washer on the hot side, it is swelling up from the very hot water, and replace the tempering valve down on the boiler...
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Old 01-24-2016, 03:20 PM   #4
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Originally Posted by ShtRnsdownhill View Post
change the washer on the hot side, it is swelling up from the very hot water, and replace the tempering valve down on the boiler...
That's clever, I like it. Unfortunately, the entirety of the hot side was re-washered and o-ringed over the summer because it was drippy. The problem existed before and since, so I didn't think to mention it.

My wife has added the additional bit of input that often it *eventually* gets hot, usually at the very tail end of your unpleasantly chilly shower. The bathroom is only about 25' from the boiler and the 1/2" lines are through a warm basement so I don't think it's an issue of patience. Something is awry. Just can't figure it.

The tempering valve at the boiler is a watts 70 series which I've learned is rebuildable... So now debating between installing a couple of fixture anti scalds at both bathroom and kitchen sink (to retain HOT water for dishwasher, washing machine, etc) vs replace the 70 with a proper temperature sensitive valve vs just rebuild the 70, which saves the hassle of draining the system and sweating out the valve body.

I will update if I find any explanation. This is mysterious to me.

Luke
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Old 01-24-2016, 03:24 PM   #5
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the super hot water is making the hot side washer expand and cut off the flow of hot water, whether a new or old washer, it doesnt matter, then the lack of hot water lets the washer cool down and the hot water flows again, if you fix the tempering valve the missing hot water should go away too...
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Old 01-24-2016, 04:41 PM   #6
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Quote:
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the super hot water is making the hot side washer expand and cut off the flow of hot water, whether a new or old washer, it doesnt matter, then the lack of hot water lets the washer cool down and the hot water flows again, if you fix the tempering valve the missing hot water should go away too...
If that were the case, though, you would expect a substantial loss in pressure at the tub/shower spigot, no? We're talking about a situation where with the cold tap at the shower control fully OFF, the temperature drops to maybe 70 (haven't measured it) with no corresponding drop in pressure. If something in the hot side of the faucet were restricting flow, the overall volume/pressure would drop.

When I draw Jr's bath tonight I will see if the sink is able to produce scalding water SIMULTANEOUS to the bath running cool water. Practically speaking, when the tub has misbehaved we have turned it off and then immediately drawn hot water from the sink into a pot and used that to make up the balance of his bath. I am wondering if the relative flow rate is an issue... The shower head is low flow, but I have to believe the sink flows even less. Perhaps it's an issue of not achieving enough heat transfer in the boiler due to excessive flow... Although that doesn't explain why it sometimes "gets better" nor why its a nonissue in summer (when the "cold" water is warmer, but the boiler temp is also governed by the low limit and therefore also colder)...
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Old 01-24-2016, 06:47 PM   #7
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When I draw Jr's bath tonight I will see if the sink is able to produce scalding water SIMULTANEOUS to the bath running cool water...
Well that was illuminating. If I leave both running wide open, they run the same barely lukewarm temp. I ran down into the basement while the taps were open. The boiler had fired, temp gauge read about 165, but the pipe running towards the bathroom was only lukewarm. So I have a problem either with heat transfer in the coil or with that tempering valve--I unfortunately did not think to feel upstream of it to see if it is having a role. I had thought it was stuck wide open but perhaps that's untrue.

I'll replace that thing, or rebuild it, and move forward from there.

Luke
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Old 01-24-2016, 07:19 PM   #8
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Are your lavatory faucets in the same bath a moan single handle?
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Old 01-25-2016, 12:16 PM   #9
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The lavatory faucet is a Delta, single handle.

I think the fact that the copper pipes running TO the bathroom are not feeling hot makes me believe the issue is at the boiler, either with the tempering valve or possibly heat transfer in the coil related to flow (though I can't quite figure that out, since it seems WORSE when the heat has been running, even though that's when the boiler temp should be higher).

I am on dad duty today and unable to deal with it, but hope to rebuild the guts of the tempering valve tomorrow. If that makes everything super hot, I will then install one of these under-the-counter themostatic valves at the kitchen sink and another where the bathroom feed goes up through the floor...

I will post an update when one exists. I have abandoned my belief that the problem is in the bathroom.
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Old 01-25-2016, 12:44 PM   #10
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when was the last time you had the coil cleaned? and the orifice checked ? the coil needs the orifice to slow the water down so it can pick up the heat from the surrounding water in the boiler..and if the coil has all kinds of crude built up on it, it acts like insulation, preventing heat transfer..coils are cleaned by ultrasonic means...you would think during heating season you would get more hot water, but for how long is the boiler at top temperature before the cold water from the heating radiators or baseboard cool down the boiler, so your heat and domestic hot water are fighting for the same heated water...when you run the hot water, does the pipe from the coil going into the tempering valve get too hot to touch?

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