very low output from electric boiler

Raimund

Howdy from Colorado,

Finally joined this site after lurking for years.

I have an issue with an old Burnham E416 electro boiler. In Slab radiant, primary/secondary piping.
9 loops 1/2"pex.
The boiler cycles trough the heating elements, the indicator lights are on and the amp-clamp shows the right draw on all elements, but it doesn't go up past 80-90F. It gets hot and hits the high limit once you close all radiant loops but for1.

The other weirdness is that there is a thermostatic mixer on the secondary loop and the boiler high limit is set to 200F.

Any chance the elements are scaled up? (from the original fill water18 years ago)
I didn't want to pull them without gaskets at hand.

My assumption at this point are:
Scaling on elements getting worse over the years till someone went in there and set the high limit to 200F to make up for lost efficiency ???
The mixer shouldn't be necessary on a electro boiler ? I always thought you can run these things down to 90F.

Any ideas from anyone versed in electric boilers, I would appreciate it

Im pushing for a new system since everything on there is from the 90's, and the electric bills are out the roof,
but still would like to now what's going on with the old dog.

Cheers
R

Jamie Hall

Wouldn't say I was versed on electric boilers -- but other forms of electric water heaters... and I would say based on that that you are on the right track with both your assumptions. And I certainly wouldn't pull them to find out without the right gaskets on hand to put them back! That never comes out will..

And I don't blame you for thinking about something else -- electricity isn't cheap, and it's not likely to get any cheaper.

EBEBRATT-Ed

You did the right thing checking with an amprobe. Scaled elements will reduce the heat transfer to the water. When they get scaled the elements will overheat and possibly fail. Next is a blown fuse or tripped breaker.

Running the boiler at a higher temp and mixing down will give you more TD between the boiler and the radiant (stored capacity) With new elements I would try running 150-160

Solid_Fuel_Man

Dont hear of many electric boilers as a primary heat source here in the US. Most are in Canada where they historically had very cheap hydropower, but that is coming to an end.

Does the boiler feed anything else? If it's just connected to the slab, then no mixing is necessary, and running it at higher temperatures would cause scale faster. That said, I've never seen a boiler scale up unless there is a lot of makeup water (leak somewhere) or the initial fill water was verrrry hard.

What are you currently (get it?) paying for electricity, per kWh? As in your total bill divided by kWh used? What is the cost of other available fuels? Oil, NG, LPG?

Raimund

It is heating radiant only. I don't see the need for the mixing valve either but I am missing the theory behind the higher ΔΤ between boiler and slab storage.
Ed, could you explain that to me?
I thought the original installer was a cast iron boiler guy and installed the mixer out of habit.
From what I understand you can run the boiler during non peak hours. I was looking at the Electro industries EB-MX, it has outdoor reset and a minimum Temp of 90F.

If it were me I'd put in a Vitodens, but alternative fuels are out of the question for them right now, due to cost and mechanical room location, they are open to a pv array.
Im still going to push the propane but really would like to understand what could be done with electric.

The fill water should be good, they're trucking in good city water, Was thinking of a small leak myself.

Thanks
R

Solid_Fuel_Man

Did you try turning off the makeup water and see if pressure holds? Is this a PEX system or some brand or EPDM rubber tubing?

Zman

It sounds like either a scaled coil or a lack of flow. Scaling seams a bit unlikely in a closed system. My money is on lack of flow caused by a high head loss thermostatic valve. How is it piped and what pumps and valves are installed?