Problem with old one pipe system on oil fired pumped CH with gravity DHW

[jimk280]

Hi Guys, called to property with oil fired pressure jet boiler. loads of people looked at it in the past apparently but not sorted it. V old one pipe system with 10 rads, some old some new. Most recent somebody renewed the circ pump which is on the CH return to boiler about 1m away. The gravity DHW side (28mm) is absolutely fine. Problem appears to be that 2 rads never get hot (1 up and 1 downstairs), and then sporadically others do not get hot then on other days do get hot. Others mainly upstairs require to be bled regularly.

Our response was to drain system, clean F&E, renew all rad valves with lockshield & TRV sets, chemically powerflush via circ pump connections.

End result not much improvement! Did notice that after bleeding all rads that the rads only really bled properly with the system off. If we tried to bleed with the system running (to push air through quicker) then there was no air escaping or water to the rads?? as soon as pump was switched off air came hissing out. Quite confusing this one.

My next step is to recommend ripping old out and fitting new fully pumped but would welcome anyone's experience on this.

Jim

Read more: http://www.ukplumbersforums.co.uk/p...pumped-ch-radiator-problem.html#ixzz2BOCM842Y

 

[dancinplumba]

did you use the correct l/s's and trv's. pump is on the return so obviously sucks air in imo

 

[kimbo]

sounds like pulling air in, check for another vent I had a similar problem and plumber had put auto air vent on system and it was sucking in air averytime pump started.

 

[stani]

Because it is a one pipe system the water will take the easy route I.e. straight round the pipes only, it's very difficult IMO to power flush a one pipe system because of the previous pipes, you also need to use specific trvs and lockshields for a one pipe system, had anyone replaced the valves on these rads before, you do need the system off to bleed air, if not the water just goes round the pipes and entrains (word of the day) air into the system.

 

[SimonG]

Try slowing the pump down as well.

 

[migoplumber]

i think your next response is the right one. if you rip the old out and install a new primary cct for him then you know what does what, the client will be guaranteed a good working system, you can agree a price, it will work. and everybody will be happy. never anypoint in playing with a system thats been bodged on bodged, if you start attempting to follow pipework and diagnose bad sizing, dodgy tees's bits of one pipe changed to two pipe you could be there for a day, and its all wasted money.
it does sound like rip out and renew properly is best course of action.

 

[WHPES]

Had a similar problem a couple of years back. Customer asked me to spend a day and I still couldn't locate the fault. Ripped out and replaced with 2 pipe system and discovered a blockage at one elbow.