baxi duo tec 28he issue

1 Dec 2019
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United Kingdom
Hi I'm at my wits end with my heating my radiators heat up upstairs but stay cold downstairs I've bleed the radiators and flushed the system as I read its usually a blockage problem unfortunately I found no blockage. I then read it could be a pump problem and due to ruling the others out even tho the pump was spinning I decided to take it out to see if anything behind had broke or come away it was fine and is in full working condition is there any suggestions on anything else I can try to fix this problem ? thanks.


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Turn off all the upstairs rads by their TRV ( or wheel head if no TRV) ,do not touch the lock shield valve on the other end of upstairs rads. See if downstairs begin to heat up.
When you took out the pump did you inspect the pump impellor for blockages in its runner?
Ditto the above advice about turning off those that get hot, then see if the others heat up.

Not wishing to be rude but being at your wits end does not normally help, as it is not always clear how far your wits normally go.
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Thanks @cross thread I will give that a check tomorrow. @terryplumb sorry should of included this yes this was one of the first things I checked they did not heat up @MeldrewsMate the reason I took the pump off was to check the impellor for blockages or too see if it was damaged it was fine
When did downstairs rads stop heating, did they all stop simultaneously ?
How many rads do not heat?
Do they have TRV's ,if so have you checked their pins are not stuck closed.
What diameter pipework goes to these rads ?
You said you have found no blockage ,what did you do to establish this and where ?
all simultaneously last Saturday when I went to turn the central heating system on yes they have trvs ive checked these taken them all off ive bleed each radiator removed each radiator cleaned them and flushed the whole system with the lock valves open. I did this as I couldn't find any other possible issues the water coming out was clean no signs of any silt sludge etc.
ill need to double check diameter but think its like 15mm - 20mm if your after the setup its feed an return not a single loop setup
When you removed each radiator ,did you open the TRV side ,and get a full flow of water from the valve ,and also from the lock shield valve as well ?
Is your system pressurised or tank fed ?
yes I did get a full flow of water from the valve and also for the lock shield valve as well the system is pressurised
When allowing water to run through each valve ,you need to keep the filling loop open and run water for several minutes to prove their is no blockage. If you don't you just drain water from pipes that have been " backfilled" through the rad from the other side ,before rad was removed ,if your with me.
Your have a circulation problem ,either the pumps at fault ,or their is a blockage on the branch to or from the downstairs rads ( either on flow or return)
I assumed you do not have heating zones ?
I did keep the filling loop open and ran it for more than several minutes
if you have any idea if what cross thread posted can cause this problem ? Im pretty sure it could be that as I had a problem with the isolation valve a year or 2 ago ill check sometime this week when I have time and post back if it fixed the issue.

I'm also fairly confident in saying there is no blockage as I flushed the system with the filling loop open. The pump I checked you could feel it I then did the screwdriver test to be sure before coming back to the pump and removing it to check the impeller was fine. hence why I'm asking for advice as almost all advice freely available only offers the pump or blockage as the problem ?

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