Hello,

I've got an old Thorn EMI Apollo (UK manufacturer, no longer made) wall mount boiler in the house that's been acting up. After the intermittent pilot sparks and lights the pilot, the main gas valve opens and buzzes continuously while the burner is lit. The gas valve is a Honeywell VR8440M2057 and is original (~30 years old).

The 24v transformer in the boiler is original but seems fine. The secondary supplies the S8610u (just replaced the old S86G last month due to no spark). The S86 makes a clean spark, and supplies 24v to the gas valve on both the PV and MV terminals as appropriate. I just replaced the thermodisc boiler temperature controls (high and low thermostat and high limit) and the wiring between the SPDT hi/lo thermostat switch and the 36T controls due to corroded terminals and excessive resistance. I was hoping the rewiring would fix the buzzing gas valve, but no luck. When I did the rewire, I also double checked all grounds and checked each bit of wire I didn't replace for excessive resistance.

At this point, I'm guessing that the gas valve solenoid is just tired.

Here are my questions:

1) Is there anything I'm missing in my troubleshooting steps?
2) It appears there are some functionally equivalent universal replacements such as the Honeywell VR8345M4302/U. Is there any reason to seek out the original part vs the universal replacement?
3) If I replace the gas valve, is there an acceptable way to adjust pressure on the new valve without a manometer? If not, will a simple digital unit like this Pyle suffice?
4) I can probably get the gas valve and a digital manometer shipped for less than the cost of the gas valve at the local parts counter. Is there any reason why a handy, careful homeowner should avoid this job?

Thanks for any help,

Jim

 

I have successfully replaced gas valves without adjusting any pressure settings on the output.

 

I do wonder if that's good advice though?

The pressure SHOULD be checked and adjusted if necessary. In a pinch you can get fairly close by carefully 'clocking' the gas meter.

 

Think about newly installed gas water heaters, ranges, ovens, outdoor grills, clothes dryers, and yard lights. Are their fuel valves adjusted? Not that I know of.

 

Most gas valves on hot water heaters, ranges, ovens, grills, dryers, etc come with the appliance and are properly calibrated from the factory. Replacement gas valves are used on a variety of applications and may need adjustment to ensure proper operation.

 

DIY,
With all do respect to trooper, Gil has a valid point. In over 30 yrs. in this business I personally have never seen one person ever clock a meter or use a manometer when they've changed a gas valve unless something very noticeable was wrong, and that includes the gas company with whom I've worked with many times.

In theory & on paper it's what should be done but never is. I've put in many myself and after checking just out of curiosity what they generally come set at is 3-4" w.c. which is what most residential units run at.

Just my opinion but if you are careful and obviously shut off your gas and make sure you have no leaks and double check everything and if you are comfortable working with gas you can do this.

I will point that this is not something I would recommend for someone who hasn't got any mechanical ability but you seem to have common sense and a working knowledge of the system.
Just remember. GAS IS SOMETHING TO BE RESPECTED.

Good Luck,

 

We said the same thing, no?

 

Jim, measure the voltage at the gas valve terminals while the unit is firing. You may have a transformer that is failing and goes into a low voltage condition when a load is applied. Also, remove and clean ALL the wire terminals and then reconnect.

 

Hey Furd, thanks for the tip. I have 26.17 volts at the gas valve between the MV and MV/PV terminals after the main valve opens. I have 26.17 volts between the PV and MV/PV terminals at the gas valve during ignition and main valve operation. I already replaced or checked resistance on every wire when I replaced the thermostat switches. I ordered a gas valve last night and plan to replace it when it arrives. I'll update the thread when I'm done.

Thanks,

Jim

 

Hey Gil,

Thanks for the info. I will be replacing the gas valve in a few days and will update the thread when done.

Jim

 

Sounds like a gas valve problem all right.

 

Thanks for the info Spott. I've got a new gas valve on the way.

As an exercise in "what should be done" I examined the documentation for the boiler, install, and new gas valve. The boiler is rated to output 30k BTU @ 2.1 in wg, 40k BTU @ 3.6 in wg, and 50k BTU @ 5.3 in wg. The install specs say the original gas valve was set to 4.3 in wg. The new gas valve is preset to 3.5 in wg.

If all that is true, would that mean the boiler would output around 40k BTU with the new gas valve installed with its default settings? Lower pressure = smaller flame, longer burn times to reach limit temperature, maybe more efficient operation and possibly adequate in all but the coldest temperatures?

Thanks,

Jim

 

Yes. Close to 40Kbtu/hr. New, replacement gas valves are normally pre-set to 3.5" W.C., which is pretty much standard. I would try it that way, and if you think it's not putting out enough heat, maybe tweak the outlet pressure a bit with a manometer.

 

DIY,
Gil is exactly right and I can't add anything to that. The fact that you read all that and are interested, is telling me you'll have no problem with this.

A small thing about the 3.5"w.c. that comes factory set. I didn't want to commit myself to that and have someone put a manometer on a new one and get a little over or under and think it's defective so I gave myself some wiggle room. That's what I guess you could call the industry standard for residential units.

Good Luck,