Downstairs rads cold and it's not the pump

Adam Everitt · Nov 26, 2016

Hi everyone,

Having a bit of a problem with my CH but have tested a few things now, wonder if anyone could narrow down the possible problems for me or suggest something else to try...

Previously had no problems with the heating for years, and it had been on the time regularly for a good 2 months before this fault occurred - system was completely untouched before the fault occurred.

Wednesday the week before last my downstairs radiators were stone cold but the upstairs ones were fine. Went through and bled all the air from rads and the valve near pump, did this over and over because since the pump was still running I assumed it could only be an air blockage, no success.

After a few days of this decided to replace the pump head, had to drain the whole system because the pump isolator valves weren't holding back any water! :32:

The old pump did have a bit of crud in the impellers but didn't stop it moving. Anyway, new pump in, system refilled, air out and it was perfect for a whole week until last night when the same problem seems to have come back!

Out of curiosity i'd been bleeding air from the rads all week and keep getting small bits of air every day in all upstairs rads and valve near pump - Something tells me that's not normal?

I'm thinking somewhere my system must be letting air in and it's creating a block, tempted to drain it all off again and refill just so we can have some heat downstairs but not sure what to try to get that permanent fix. Does this suggest a leak somewhere? Anyone suggest anything else I might want to try?

Thanks in advance,

SimonG · Nov 26, 2016

Pumps goosed. Your system is full of crap and the new pumps don't like it.

Last Plumber · Nov 26, 2016

I agree with SimonG.
If the impeller was blocked on the last it could have become blocked on the new one.
Which pump is it, a lot of the new ones are very sensitive and don't like any kind of restriction at all

SimonG · Nov 26, 2016

So when you drained down did you change pump valves or just drain and swap head. If the latter there's your issue.

Adam Everitt · Nov 26, 2016

The pump is a Grundfos UPS 15-50.

Didn't change the valves as these were originally fully open anyway so left them the same, do i need to restrict anywhere?

I wonder if it's worth draining it again and checking the pump for crud... but that won't explain the air I was getting thru the week. As you suggested SimonG I might have a look at getting the rads pressure cleaned..

e2a
Draining water off at one of the downstairs radiators - no air at all just warm water? very sooty black warm water and it was only refilled a week ago... is this my problem?

PlumbBobBob · Nov 26, 2016

sludged water = very dirty system

Frog67 · Nov 26, 2016

As above. may be worth power flushing the system, chances are the sludge has started blocking the pipework. Expansion pipe may be blocked and forcing air to be drawn down the vent or Hydrogen gas is forming inside the rads.
If the pump is knackered then the other controls ie zone valves / boiler wont be too healthy either.

Adam Everitt · Nov 27, 2016

hi all, thanks for all the feedback and ideas.

Pretty sure a magnet should never stick to the pipework....:rofl:?
This is where the expansion tank meets the hot water returning before entering pump - where i found debris previously

Think I might need to cut this piece out and replace before a good power flush, thoughts? e2a and a service on the boiler and someone round to inspect the zone valves?