Indirect fired water heater hot water coil leaks:

What is an "indirect" fired water heater coil leak and how can leaks at the hot water tank cause the heating boiler to be placed at over-pressure causing in turn leaks at the boilers temperature & pressure relief valve.

How do we detect this condition, why is it dangerous, and how is it repaired?

Internal Leaks in an Indirect Water Heater's Hot Water Heating Coil

An indirect water heater is a hot water tank system whose water is heated by circulating water from a separate building heating boiler thorugh a heat exchanger coil inserted into the hot water tank. This turns the concept of tankess coils inside out.

Thanks to Carson Dunlop Associates, a Toronto Home Inspection Firm and Home Inspection Educator, for permission to use sketches shown in this article.

In an indirect water heater it is boiler water (not building potable water) circulating from and back to the heating boiler that heats a volume of water stored in the hot water tank.

See INDIRECT FIRED WATER HEATERS for details.

Our page top photo shows an Alliance indirect hot water heating system from Burnham. Look around the oil-fired hydronic heating boiler in the left of the photograph. This boiler is providing hot water that circulates through the heating coil inside the Alliance indirect water heater.

We found water around the floor of the heating boiler not at the hot water tank itself. What was going on? Leaks at the TPR valve were wetting the floor around the boiler. Several problems can cause pressure/temperature relief valve leaks. One of them is an internal or hidden leak in the indirect fired water heaters coil that resides inside of the hot water tank.

You can't see this leak but you can see its effects.

Building water supply pressures pressures inside the hot water tank, calorifier, cylinder or geyser (depending on where you live) are normally higher than pressures inside the heating boiler.

Therefore a leak in the heat exchanger coil used in an indirect water heater will normally send building water supply water (potable water) into the heating boiler and its piping system, entering at the coil leak and passing into the piping that connects the coil inlet and outlet to the heating boiler.

Thus pressures in the heating boiler will increase. This will show up as higher or abnormally high pressures on the heating boiler's pressure gauge, and the leakage will ultimately cause dripping or discharge at the boiler's temperature and pressure relief valve or TPR valve.

See RELIEF VALVE LEAKS

Watch out: under normal conditions, because building water supply pressures are above boiler pressures, an internal leak in the indirect water heater's heat exchanger coil will cause boiler pressures to rise. But there can be exceptions in the direction of water leakage, as we explain

at TANKLESS COIL LEAK DIRECTION IN or OUT

Other types of leaks found at indirect fired water heaters are discussed

at INDIRECT FIRED WATER HEATERS

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-11-29 - by (mod) -

Mark

That temp-fix for domestic hot water is presuming that the problem is that the aquastat or "thermostat" that controls your hot water is not working -
of course the problem could be something else like a circulator pump or circulator pump control relay.

I'm not sure what controls are on your water heating system nor how your hot water is being made or stored.

Is it:
a tankless coil in the boiler - if so these suggestions are irrelevant and the problem is perhaps a bad mixing avlve

or an indirect fired water heater - in which case an aquastat on the hot water storage tank switches the circulator on and off

or a separate water heater having nothing to do with your home heating system

On 2020-11-29 by mark

Recently we lost hot water to the sinks and showers in our home even though the boiler still heats the house.

A plumber friend suggested a jumper wire to bypass the thermostat for the boilermate to regain hot water till we are able to address the actual problem. Is this possible and if so where do I locate the terminals for the thermostat.

On 2020-11-06 - by (mod) -

Normally you would use brass in between copper and steel

On 2020-11-05 by Ken

On a glass lined steel tank and coil indirect fired water heater, what material nipple (black pipe, galvanized, brass, etc.) would you use to connect the boiler supply and return. I want to minimize galvanic corrosion at the connection to the coil. I was thinking black pipe nipple then dielectric union to copper.

On 2020-04-30 - by (mod) -

Margaret

If the leak is at an external connection to the coil then it's an ordinary plumbing repair using new fittings and pipe sealalnt.

If the leak is in the coil itself, although there are "stop leak" products sold to run through heating boilers that can stop small leaks, I don't recommend that approach as in my opinion in this application the repair is not likely to be durable. Instead, unfortunately, it's time to replace the coil.

On 2020-04-30 by Margaret kirwan

How to fix a leak on a coil in an indirect water heating g cylinder

On 2018-12-02 by LFOD 18

Burnham boiler and indirect water heater issues. Getting hot water in the cold water feed line down the side of the water heater and in the cold water side of the mixing valve at the top of the water heater. There is also increased pressure at the boiler ranging from 30-38 psi at different times.

The boiler PRV "weeps" on and off. Plumbing and heating technician believes that there could be a leak in the indirect coils inside the water heater causing and that potable water may be leaking into the closed boiler system and that boiler water may be leaking back into the water heater tank and infiltrating the cold water feed line.

What causes the cold feed line to get very hot all the way back up to the expansion tank? Does this sound like a possible leak in the internal coil of the water heater?

On 2018-02-13 - by (mod) -

Anon

Since the indirect fired water heater tank is normally always full of water, if yours is losing water there must be a leak in or near the tank combined with a failure in the cold water inlet line or valve that's not keeping the tank full. To me this does not quite add-up. I think we don't have the full picture.

On 2018-02-13 by Anonymous

My indirect storage tank keeps loosing water why is this

On 2016-10-11 by Anonymous

The hot water is not as hot as it used to be.

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Continue reading  at TANKLESS COIL LEAK DIRECTION IN or OUT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• RELIEF VALVE LEAKS
• TANKLESS COIL / HOT WATER COIL LEAKS
  • TANKLESS COIL EXTERNAL LEAK SPOTS
  • TANKLESS COIL EXTERNAL LEAK EVALUATION
  • TANKLESS COIL RUST TYPES: SUPERFICIAL vs EXFOLIATION
  • TANKLESS COIL INTERNAL LEAKS INTO the BOILER
  • INDIRECT WATER HEATER COIL LEAKS INTO the BOILER
  • TANKLESS COIL LEAK DIRECTION IN or OUT
  • EVIDENCE of TANKLESS INTERNAL COIL LEAK INTO BOILER / WATER TANK
  • REPAIR OPTIONS for TANKLESS COIL LEAKS

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

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INDIRECT WATER HEATER COIL LEAKS INTO the BOILER at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to WATER HEATERS

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