Combi Water Temp Goes From Scalding to Luke Warm!


Postby hairyjockman » Sat Feb 02, 2019 10:13 am

Some help with how water system on Ariston EuroCombi SX20. Ttter ye not folks! 20 Years old this month and generally trouble free all that time.
Parts replaced since new: 3 x pumps (1 failed in warranty), 2 x diverters, 1 x pcb and a new gas valve 6 months ago – not bad eh?
Current issue – water not hot enough – never been a prob before and yes the thermo is turned up full where it was set for last 20 years at 40% - beyond that it was scalding esp in shower.
System set up as follows – all on 1 floor and in a straight line. Boiler is 12 feet from kitchen sink where water will literally melt your skin off. The bathroom sink is a futher 6 feet, again water will melt your skin but only if flow is very low. Bath & shower (next to each other) a further 6 feet away. Shower has thermostatic valve and was always scalding now it’s at best luke warm and you can forget about running a bath – especially with these outside temps in mid winter.
Initially only had a prob with heating and turned out previous fitter who changed the gas valve had blanked off vac tube in gas valve and reading were well off – gas pressure was sky high. After correctly setting up to the factory specs (it’s now got British Gas maint contract) the heating system now hits 88c but takes 3 hours to get there.
Whist, with me watching on, setting up I heard the fitter phone his mate and ask how toturn the pump down to no 2 it’s at 3! As far as I am aware, rightly or wrongly, you cannot change pump speed – only regulate flow via diverter valve – correct?
So my thinking is the boiler is running ok but the flow of hot water is not fast enough to overcome the mains pressure of the cold water hence when it gets further from boiler the more the cold water overrides the hot water temp? When tap running at “normal” flow in bathroom sink & shower the temp gauge on boiler shows ub 60 degrees. Slow the flow and it shoots to 88+ in sink but not in bath or shower.
If so, hot to get it back up again – increase the gas pressure???? Or the flow from divertor (if so the blue fitting on top of divi is it turned clockwise or anti clock to increase?) or is there something else I am missing?
Help much appreciated folks as the shower is bloody uncomfortable…
hairyjockman
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Postby hairyjockman » Mon Feb 04, 2019 9:30 am

OK - so nobody up for an answer here?
Should have mentioned - cold water flow is 29lit/min, hot water at nearest point to boiler being kitchen tap is 8.6lit/min with zero deg rise.
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Postby ericmark » Thu Feb 07, 2019 5:34 pm

I wonder where my answer went? I think your boiler is modulating, it should modulate of course, but only when water is warm enough.

The boiler will likely have an output of between 8 and 28 kW, and is controlled by return water temperature, either from heat exchanger or central heating. So likely something is either causing a restriction or the lock shield valves are not set correct.
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Postby hairyjockman » Fri Feb 08, 2019 9:09 am

....could it be a heat exchanger blockage????
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