I have an old house with hot water hydronic heating. Boiler is an AO Smith HW 160 P770, natural gas, looks like 1980 manu date.

Last spring when I turned off the boiler for the summer it was working fine, with one minor exception (see below). I don't turn it off but turn the water temp to as low as possible and set the thermostat so the water doesn't circulate.

When I went to restart the heat this summer I checked everything and turned up the temperature on the boiler and the burners did not kick on. I cycled the power, still nothing.

If I turn the thermostat up the water does circulate - note I need a new impeller for my pump, but intend to get a Taco 007 once I get the boiler working again - but no heat.

I assume this is the relay/switch box on the outside of the boiler causing this. I need trouble shooting steps and potential replacement recommendations.

thanks!

Seattle-kk

PS - great forum!

 

According to the title of your post, the natural gas flows? And the burner doesn't light? I hope this is a misunderstanding, because that would be a time bomb.

Your boiler is c. 1980, so I assume it has a standing pilot? Is the pilot lighted?

 

Sorry I was not more clear.

Yes the pilot light is lit, which is why I said 'gas is flowing'.

when I adjust the water-temperature dial, on the boiler, it doesn't "click" like it used to and the burner's don't light up, and, it seems, that no gas is flowing to the burners.

I assume the box with the wires coming in and out of it, on the front of the boiler, is a relay/control box and it would seem that this box is not sending the signal for the burners to heat the water.

I've attached a couple of pics.

thanks for your help

 

Your first photo shows the gas fuel valve. For the burners to fire, you must have 24VAC across the valve's two terminals with wires connected. Do you? If you do, and the burners don't light, then that would indicate there is something wrong with the gas valve itself.

If you don't have 24V at the fuel valve when the burners are supposed to fire, then you need to troubleshoot with a multimeter, and find out where the 24V is being lost. Start at the 24-V control transformer, and work toward the gas valve in a systematic manner. The problem could be anywhere in the 24-V control circuit between the transformer and the gas valve, so systematic troubleshooting is called for. If there is a wiring schematic pasted somewhere in or on your boiler, that could help troubleshooting - otherwise, just trace the 24-V wiring from the transformer secondary.

 

Can you maybe get a better lighted shot of the control/relay box?

Is there a make/model on that control? Maybe inside the cover on a label?

Do you own a multimeter and know how to use it?

Sorry if I'm repeating what Gil is asking... didn't see his post before I posted.

If there is a wiring diagram on the boiler, see if you can get a CLEAR photo and post that. Since the forum resizes uploaded pics, you might have to set up a free account at Photo and image hosting, free photo galleries, photo editing and upload a high res photo there in order for us to be able to read it.

 

Thanks for the replies.

Yes I have a multimeter and Yes I know how to use, thanks.


No model number that I can see on the relay/control box, but I'll check again.

I'll report back after checking for 24v as suggested.

Are new control-box relays easily available and if so what do you-all recommend.

thanks!

 

Could be easy enough... or more difficult...

Easy would be if the 'immersion well' behind the existing control will accept a modern aquastat control.

More difficult would be if you had to change the immersion well to suit a newer control.

Can I ask why your practice of turning down the temperature control each Spring? As long as you turn the thermotat down, I would think it wouldn't matter...

OR, does your boiler 'free run'? In other words, keep itself hot 24/7 and the thermostat only controls the circulator?

I can't find any documentation on the web for your boiler.

 

Resist the temptation to start replacing parts unless you have pinpointed the precise problem. But, to answer your question, relays, if that is your problem, which I doubt, are $15 a dozen.

My thinking is that there may be no relay in the 24-V circuit controlling the gas valve - particularly if the boiler was set up for warm start (i.e., it stays warm continuously during the heating season). If so, it would be 24V from the transformer, in series through the aquastat, and then to the fuel valve. If it is cold start, then the thermostat/pump circuit would be in the picture, too.

The relay box you are suspicious of, clearly controls the circulator pump - which you say works when called for. Don't jump to conclusions - you will waste time and money.

 

Good question. My practice is to turn the gas valve to OFF, which douses the pilot, too. Then shut the manual gas valve ahead of the 24-V fuel valve. Leave the wall thermostat wherever you want until fall. Turn your thermostat to "cool" if you have central air.

 

Thanks for your help guys (and gals if there are any gals here).

Figured out, with your help, that the thermostat does control circulation and heating the boiler. Once I let the thermostat stay up for awhile I got circulating hot water.

Other issue I still have is a loud pipe-banging like sound when the circulating pump kicks on. it's not the hammer-hammer sound of the coupler, I've replaced that before, sounds like someone hitting the pipes with a metal hammer.

I took my auto-mechanic stethoscope (no I'm not an auto mechanic but I DIY my own cars) and listened and the sound is coming from near the impeller.

Next step is to do the annual drain and refill of the systems followed by bleeding all radiators and we'll see if banging is air or a blown impeller.

If the impeller is bad I intend to replace the pump/impeller with a Taco 007


thanks again,

Seattle-KK

 

Hang on a sec... are you saying that you drain and refill the system annually? Yes, I think you are.

DON'T DO THAT! There is absolutely NO REASON to do so. It will not improve anything, and in fact will cause more harm than good, and it's just plain extra work that is not needed.

The harm that it does is in the fact that the fresh water has OXYGEN in it and every time you do that, you are causing rust and corrosion to all the ferrous metals in the system.

Leave that old stanky oxygen starved water in the boiler... it won't heat any better with fresh water.

 

The banging could be air... could possibly be 'cavitation' (I don't think so though)... what else?... must be another reason out there...

 

How messed up is the pressure and temperature gauge?

I doubt it's accurate, but tell us the readings on the gauge.