Combi boiler DHW filter clogged signs in Greater Vancouver

A combi boiler has a small filter or screen on its domestic hot-water inlet that catches debris and scale before they reach the plate heat exchanger. When that screen clogs, your hot water suffers in fairly predictable ways. Here is how to recognize a blocked DHW filter and what to do about it.

Signs the DHW inlet filter is clogging

The clearest symptom is weakening hot-water flow that develops gradually rather than overnight. As the screen fills with grit and scale, less water reaches the domestic heat exchanger, so showers thin out and tubs fill more slowly even though cold flow stays normal.

Because a combi needs a minimum flow to fire, a heavily clogged screen can also drop the flow below the trigger point, leaving you with intermittent cold spells. You may notice the hot water is fine when nothing else is running but fades quickly under any extra demand.

• Hot-water flow that drops while cold flow stays normal
• A gradual decline over weeks or months
• Hot water cutting out intermittently as flow nears the trigger rate
• Weaker hot water that worsens when a second tap opens

What you can check and what to leave to a pro

First rule out the simple stuff at the fixtures: descale shower heads and aerators and confirm the issue affects hot water specifically. If cold flow is also weak, the problem is more likely household pressure than the filter.

The DHW inlet screen sits inside the boiler's plumbing and clearing it involves isolating and opening the unit, so it is a job for a licensed technician. During a service visit, the screen can be cleaned or replaced and the domestic heat exchanger inspected for scale at the same time, which is the more thorough fix in harder-water pockets of the region.

• Descale fixtures first to rule out a simple restriction
• Check whether cold flow is also affected
• Have a technician clean or replace the inlet screen
• Combine it with a heat-exchanger inspection

Frequently Asked Questions

What does a clogged DHW filter do to my hot water?

It restricts the water reaching the domestic heat exchanger, so hot-water flow weakens and can cut out, while cold-water flow stays normal.

Can I clean the DHW inlet screen myself?

It is inside the boiler's plumbing and requires isolating and opening the unit, so it should be left to a licensed technician who can do it safely.

How do I tell a clogged filter from low pressure?

If only hot-water flow is weak and cold is fine, suspect the filter or heat exchanger. If both hot and cold are weak, the issue is more likely household water pressure.

How often should the filter be checked?

A check during routine annual servicing is sensible, and more often if you notice hot-water flow steadily declining. Local water conditions influence how quickly it fills.

HeatLand Heating & Cooling is a licensed and insured, TSBC-certified HVAC company serving homeowners across Greater Vancouver. Our technicians diagnose the real fault, explain your options in plain language, and complete the work safely and to code.

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