Open vented system

[Mutu]

Hi guys,
Im new to this forum so hi and please bare with me. I recently power flushed an open vented central heating system. After testing system and adding inhibitor all worked well for a week or so. Boiler is roughly 5 yrs old(Gloworm) but rads and valves quite dated. Anyway after a week or so customer phoned and said new bathroom towel rad not heating up. Suspecting an airlock I shut other valves down and said towel rail heated up. All fine...till 3 days later the whole ground floor of 4 rads not heating up. I returned and shut all rad valves down upstairs forcing heating downstairs and all worked fine again... For 4 days. Customer phoned saying boiler making a lot of noise and no rads heating up. I've tried everything but with no joy. Every rad been bled countless times. Sounded like boiler was Ketteling but turned temp down on boiler from 75 to 65 and that seems fine

Any assistance greatly appreciated.

 

[gassafe]

We're these existing problems or "since you powerflushed the system"?

If the glow worm boiler was Ketteling then it may still have sludge in it, it's difficult to get all the crap out of them spiral type vaillant heat exchangers!!

cold feed & vent okay, no pumping over etc?

 

[Mutu]

Hey gassafe

Cheers for the quick reply! These are new issues and also used the double magna clean big boys on system for a full 12hrs. I stopped to clean them out 4 times till spotless
cold feed and vent okay and pump seems good. Double checked height of vent to f&e too. Really don't wanna put mains on a open vented system unless its last chance saloon! Very wierd though I was there yesterday and while playing with the pump in cylinder cupboard heard the hot water cylinder almost boiling. Homeowner away on holiday and dhw turned off at controller
opened a hot water tap and literally burned my hand it was nearly boiling
checked 2port valve, it's fine
losing my mind

 

[steadyon]

Think I'd be suspecting the DHW zone valve. How else would the hot water be that hot (unless they've left the immersion on) unless there is hot water circulating in the coil. When you checked it, did you take the head off and make sure the valve itself was actually closing?

If the coil and /or a bypass were well clogged before the flush, maybe you've cleaned it so well its now passing all the primary water?.

 

[gassafe]

Must have been pretty bad to have the magnacleanse filters full up 4 times!!!

It does seem the system is running too hot, maybe the boiler thermistor faulty, plus check the cyl stat & 2 port if the hw is that hot as it sounds dangerous!

 

[Paulplumb]

where did you flush from? If it wasn't the pump might be worth taking the head off and inspecting.