FAQ
TL;DR: If your De Dietrich DTG 111-5 NEZ has hot DHW but cold radiators, start with circulation: bleed the pump, set it to "3rd gear," and check for a stuck valve. "The CO filter may be clogged." [Elektroda, dobroslaw, post #16777410]
Why it matters:** Quick circulation checks can restore heat fast and avoid emergency call-outs. This FAQ helps homeowners fix cold radiators when DHW still works.
Quick Facts
- Reported system pressure: 1.8 bar; heating still failed, so pressure alone isn't the issue. [Elektroda, rodick, post #16776935]
- Common culprits cited: clogged CO filter or faulty three-way valve switching. [Elektroda, 762302, post #16777269]
- Pump can sound OK while the impeller is off, giving zero flow. [Elektroda, wojtek1234321, post #16777233]
- Quick fixes: bleed the pump, set speed to gear 3, and check the spring check-valve for jam. [Elektroda, dobroslaw, post #16777410]
- Root cause in this thread: a bad circulation pump confirmed by the OP. [Elektroda, rodick, post #16779384]
How do I fix De Dietrich radiators that stay cold in winter mode but DHW is hot?
Verify valves are open, then focus on circulation. Check the CO filter and three-way valve, and consider a simple power reset. If lines after the pump are cold, suspect blockage or pump failure. Start with easy steps before calling service. “The CO filter may be clogged.” [Elektroda, 762302, post #16777269]
Where do I check heating-system pressure if my boiler has no gauge?
Look on the installation near the boiler, not on the boiler fascia. The pressure gauge is typically fitted in-line close to the appliance, as noted in the discussion about checking pressure outside the unit. [Elektroda, 762302, post #16776893]
What pressure is considered OK in this scenario?
In the reported case, the system showed 1.8 bar and domestic hot water worked. That suggested pressure was adequate and the fault lay in circulation or component switching, not fill pressure. [Elektroda, rodick, post #16776935]
DHW works but radiators and risers are cold—what does that indicate?
That points to no circulation through the heating loop. The poster heard the pump, yet the pipe after the pump stayed cold. That symptom aligns with blockage, a stuck valve, or a failed pump that spins but does not move water. [Elektroda, rodick, post #16777201]
Could a closed heating (CO) valve be the whole problem?
Yes. A closed circuit valve will keep radiators cold even if the boiler and DHW operate. Confirm that every isolation valve on the heating flow and return is fully open before deeper diagnostics. [Elektroda, 762302, post #16777135]
My pump hums, but no heat reaches radiators—what fails in this edge case?
The motor can run while the impeller (rotor) is off or stuck, delivering zero flow. This deceptive failure makes pipes after the pump stay cold although you hear the motor. It requires inspection or pump replacement. [Elektroda, wojtek1234321, post #16777233]
How do I bleed a heating pump and set its speed?
Loosen the central screw until air hisses, then retighten when water appears. Set the circulator to speed gear 3 to restore flow after air removal. If a nearby check valve is jammed, replace it with a metal-plug type. [Elektroda, dobroslaw, post #16777410]
What is a three-way valve and why can it stop heating?
A three-way valve diverts hot water between DHW and the radiator circuit. If it sticks toward DHW, your taps stay hot but radiators remain cold. Inspect or service it when winter mode gives no space heating. [Elektroda, 762302, post #16777269]
Should I try a boiler reset before calling service?
Yes. Cut power for about 3 minutes, then restore it to reboot controls. This basic reset can clear control hiccups after summer or power events and is quick to try during troubleshooting. [Elektroda, 762302, post #16777412]
How can I tell if there’s at least some gravity circulation?
Feel pipes near the boiler and before the pump. With no active circulation, a bit of heat might still rise by gravity. If everything stays cold, you likely have a complete flow stoppage or failed pump. [Elektroda, kossy77, post #16777463]
Do I need a room controller for the boiler to heat in winter mode?
No. The case discussed lacked a room controller, yet heating should still work in winter mode. Controller absence was not the root cause; circulation faults were. [Elektroda, rodick, post #16776781]
What finally fixed the issue in this thread?
The homeowner confirmed a faulty circulation pump. Replacing or repairing the pump is the durable fix when the motor runs but heat never reaches radiators. [Elektroda, rodick, post #16779384]
Could a clogged CO filter alone stop heating?
Yes. A clogged central-heating (CO) filter can choke flow so radiators stay cold while the boiler and DHW seem fine. Clean or replace the filter when you notice no heat beyond the pump. [Elektroda, 762302, post #16777269]
What is a check valve and how can it fail here?
A check valve lets water flow one way in the loop. If its plug jams, flow stops and radiators stay cold. The thread recommends replacing jammed units with metal-plug versions to resist clogging. [Elektroda, dobroslaw, post #16777410]
Any quick 3-step plan I can follow before calling a technician?
- Kill power for 3 minutes, then restore it to reset controls.
- Bleed the pump and set it to gear 3 to purge air.
- Check and clean the CO filter; inspect the check valve for jams.
[Elektroda, dobroslaw, post #16777410]
If pressure reads fine, what should I check next?
Move on to flow components. With 1.8 bar reported and DHW hot, focus on circulation: pump operation, filters, three-way valve, and check valve function. [Elektroda, rodick, post #16776935]
