Plate heat exchanger from above, four flanged ports on the fixed end plate with lever-operated isolating valves around it

Exchanger and valves — Inzonex Modular Insulation, hot-water skid

Heat exchangers / Faults

Heat exchanger faults

Almost every complaint about an exchanger is one of four things.

Not enough heat, a leak, a blockage, or the two circuits finding each other. They present differently, and the gauges and valves already on the skid diagnose all four. That is the argument for keeping those readable rather than buried. What follows is the order the checks are usually made in.

Not enough heat

The common complaint

Fouled, or never big enough

A unit that has slowly got worse is fouled. A unit that has never made temperature is undersized or plumbed wrong. Commissioning figures settle it in a minute. Without them, an approach temperature that is wide but stable points at sizing, and one that is widening points at fouling.

Check the flow before the unit

A blocked strainer, a valve someone left part-shut, or a pump running at reduced speed. From the far end of the building all three look exactly like a failed exchanger. Open the strainer first, not the exchanger.

Countercurrent, both ways round

A unit piped co-current instead of countercurrent loses a large part of its capacity and nothing about it looks wrong. On a unit that has never performed, the direction of both circuits is worth confirming.

Leaks

Where, and what it means

To atmosphere at the pack

A gasket that has hardened, relaxed or been pinched. It shows as a drip at the plate edge. Tightening the tie bars past the nameplate dimension will not fix it, and it crushes the rest of the gaskets.

At the ports

The flanged connections into the fixed end plate, which are ordinary flanged joints with ordinary gaskets and are treated as such.

Between the circuits

The serious one: a cracked or corroded plate letting the primary into the secondary. It shows as pressure or chemistry crossing where it should not. Each side is isolated and pressure tested separately, and a cracked plate is replaced, not repaired.

Blockage

When something arrives in the channel

The channels are narrow

Narrow channels make the unit efficient and make it intolerant. Debris that passes a pump will stop in a plate channel, and it usually arrives after work upstream rather than by itself.

The strainer is part of the exchanger

The Y-strainer and the dirt separator ahead of the unit are not separate equipment as far as this fault is concerned. A blocked exchanger with a clean strainer is unusual enough to be worth questioning.

What insulation has to do with it

Keeping the diagnosis possible

Gauges have to be readable

Every check above is made on a pressure or temperature reading at the unit. Insulation that covers a gauge or a test point does not get lifted for a reading - the reading simply stops being taken.

A weeping joint under lagging is invisible

The insulation absorbs the leak and holds it against the steel, so the first sign is not a drip but a failure. Ports and gauges stay outside the module for that reason.

Reference

Fault against first check

Fault	Usual cause	What to check first
Gradual loss of output	Fouling on the plates	Approach temperature against commissioning
Never made temperature	Undersized, or piped co-current	Flow direction on both circuits
Sudden loss of output	Blocked strainer or channel	Open the strainer first
Drip at the plate edge	Gasket hardened, relaxed or pinched	Plate-pack dimension against the nameplate
Circuits contaminating each other	Cracked or corroded plate	Isolate and pressure test each side

Fault · Usual cause · What to check first

Asked about heat exchanger faults

Questions.

Answers distinguish modelled heat-loss estimates from equipment selection and service guidance.

Why is my heat exchanger not producing enough heat?

If it has got worse over time it is fouled. If it has never made temperature it is undersized or piped wrong. A unit connected co-current instead of countercurrent loses a large part of its capacity. Before either, check the strainer and the flow. A part-shut valve looks identical from the far end of the building.

What does it mean when a plate heat exchanger leaks?

At the plate edge it is a gasket, hardened or relaxed or pinched during assembly. At the ports it is an ordinary flanged joint. If the two circuits are contaminating each other it is a cracked or corroded plate. Isolate the unit, pressure test each side, and replace the plate.

Can you fix a leaking heat exchanger by tightening it?

Only if the pack is genuinely slack against the nameplate dimension. Pulling it past that figure to chase a leak crushes every other gasket in the pack and turns one leak into several. If it is already at dimension, the pack comes apart.

How do I tell a fouled exchanger from an undersized one?

By whether the approach temperature is moving. Wide but stable, and it was never big enough. Wide and still widening, and it is fouling. The commissioning figures make this a one-minute check. That is the argument for keeping them somewhere other than a folder that left with the contractor.