Ascent Combi and Ascent Plus Combi Gas – January 2024 25
HOT WATER DIAGNOSTICS
First, test hot water at a simple fixture like a sink instead of a shower. Most hot water issues are corrected by the following:
1) Properly setting the mixing valve (usually between 4 and 5 ½ which is 120°F to 125°F maximum). Setting higher
temperatures may cause fluctuations.
2) Making sure the boiler low limit temperatures is set to 170°F and not lower.
3) Making sure the burner primary control has a 3 second pre-purge.
4) Fluctuating domestic mixed temperatures may be caused by debris obstructed check valves or the shuttle on the
mixing valve (see page 2). Continuously move the set point up and down through the full range when cleaning or
flushing.
5) “Bucket test” the hot water flow to make sure it does not exceed the boiler capacity.
6) Make sure the heating circulator has a functioning check valve. This issue may only show up during the heating
season.
If these do not correct the hot water condition, check to see if the domestic supply temperature is adequate out of the
mixing valve at the boiler. If this is consistent and hot enough and the fixtures are not, the problem is with the domestic hot
water fixtures or hot water distribution system. Investigate any newly installed fixtures, washing machine connections, etc.
for bypassing and proper operation.
ADVANCED DIAGNOSTICS
Check boiler supply temperature at hydrostat. If always greater than 140°F, then the boiler is doing its job and you can look
at the domestic water system or potential issues with heating zones.
A short cycling boiler with long off cycles may indicate a blocked heat exchanger. Cold returns on the hydronic side
indicate a blocked hydronic side; check and clean the Y-strainer. High return temperatures on the hydronic side
indicate a blocked domestic hot water side; clean the heat exchanger and check and clean the mixing valve and mixing
valve check valves.
Check for missing or non-functioning heating circulator check valve(s). This is best performed with cold heating system
piping.
1) Heat the boiler up to limit temperature, and then remove all heat and hot water calls and close all heating zone
ball valves. The circulator will continue to run for 5 minutes.
2) Wait about 2 minutes for the temperature to stabilize on the Hydrostat.
3) Monitor the temperature at the Y-strainer with a temperature probe.
4) Manually open all the zone valves and heating zone ball valves. The temperature should remain stable. If the
temperature drops noticeably, the check valve is missing. For zone circulators, identify the missing check valve
by testing one zone at a time.
B
ass drain
Shown with optional
clean in place valves
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