Sika

Sika flow switches for pool heaters

A pool heater is only allowed to switch on when water is actually moving through it. That decision is made by a small, inexpensive component screwed into the heater body or the pipework beside it: the flow switch. Here you will find the Sika flow switch used on Optima Compact heaters, supplied with a 24 mm thread under the reference SP-107-B. It is the part most often replaced when a heater refuses to start, cuts out shortly after starting, or reports a flow fault even though the pump is clearly running.

What a flow switch does and why it fails

Inside the fitting sits a paddle or a magnetic float that is pushed by the passing water. Once the flow is strong enough, a reed contact closes and the heater control board sees permission to energise the element or compressor. When circulation stops, the contact opens and heating stops with it. Without that interlock a heater can continue to heat a static column of water, which is exactly the situation the switch exists to prevent.

Failures are usually mechanical or electrical rather than dramatic:

• Scale and debris – calcium deposits or sand and hair past a torn filter can stiffen the paddle so it no longer moves freely.
• Fatigue of the reed contact – after years of switching the contact may stay open, or weld closed, giving either a permanent no-flow error or no protection at all.
• Leaking thread – a seal that has hardened, or a thread that has been overtightened in the past, leads to weeping around the body.
• Cable and connector damage – the thin two-core lead is exposed to damp and to UV in an open plant room, and chafes where it is routed.

Because a failed switch mimics a failed heater, it is worth testing before condemning anything more expensive. With the power isolated, a continuity check across the two leads should show the circuit opening and closing as the pump is started and stopped.

Choosing and fitting the right switch

Flow switches look alike, so the selection comes down to a handful of measurable details rather than appearance. Before ordering, check the following against the part you are removing:

• Mida de la rosca – the SP-107-B is listed with a 24 mm thread; measure the external diameter of the threaded boss on the old switch rather than guessing from the pipe diameter.
• Overall paddle or body length – the sensing element has to sit in the flow without touching the opposite wall of the housing, so compare lengths side by side.
• Heater model – the Optima Compact range is the intended application; if your unit is a different model, confirm the reference printed on the switch body or shown in the exploded view of the manual.
• Position number – most heater manuals number each component on a parts diagram. Quoting that number alongside the model name is the quickest way to be certain you are looking at the same item.
• Cable and terminal type – note whether the original has flying leads or a plug, and how long the lead needs to be to reach the control board.

On installation, isolate power and water, drain the section of pipework, and fit the switch so that any flow-direction marking on the body matches the direction of travel. Seal the thread with PTFE tape or a suitable thread sealant and tighten by hand plus a modest turn with a spanner; plastic housings are easily cracked. Refill, run the pump and check for weeping before restoring power, then confirm that the heater starts only with the pump running and stops promptly when it is switched off.

Sika at PoolParthub.com

Here we list the Sika flow switch for Optima Compact heaters, reference SP-107-B with a 24 mm thread, as a single, clearly identified item rather than a vague universal substitute. Sensors of this type are a standard service part, and matching the thread and the original reference removes most of the guesswork that comes with a plumbing-counter replacement.

The aim across the site is to keep working equipment in service instead of replacing a whole heater because one safety contact has stopped closing. If you are unsure whether this is the switch fitted to your unit, compare the thread diameter and the marking on the old body with the product details above, and check the parts diagram in your heater manual for the corresponding position number.