Radiators cold, but heating on...

[summat]

Hi, new poster, and a DIYer that just doesn't understand water.

I've a 20 year old house with Y-plan system, bit of a Trigger's broom (I've previously separately replaced the pump, 3-port valve, cylinder, plumber replaced the boiler... but the pipe-work is all original!) Oh, 12mm microbore plastic to the rads.

Pump is < 6 months old, and a new magnaflow installed at the same time. I power-flushed the system whilst replacing these, and cleaned/inhibited the system whilst doing this. Until recently - all has worked well.

Today, no heating. Well, a little from the upstairs bathroom rad (this is a bypass), but nothing significant from the others. I've bleed the ground floor rads (no air expelled) and tried opening the two lower bleed valves (lowest parts of the system) - some discoloured water but no sludge.

Previously when I power-flushed the system (6 months ago, when replacing the pump) there was lots of magnatite (or whatever it's called) but after a couple of hours the system ran clear.

I know that I can feel the heat hit the CH side of the 3-port if I turn the CH off, leave to cool, then turn CH on (pipe heats up in seconds to hot). Thermostat is generating demand. 3-port can be heard motoring when alternating between hot water/CH. But no heating!?

I'm thinking it's time to power-flush again (at least that justifies me buying the second-hand unit last year) - as all I can imagine now is a blocked manifold, but would happily try anything easier if anyone has any clever idea?

 

[kris]

Dependind how the system was refilled it maybe air or gunk , I don't do powerflushing as don't have a machine but I always thought u couldn't flush microbore pipework,
Take it your system is gravity fed, are all valves open or balanced , has pump been bled and pump valves defo fully open ,,, Defo a bad circulation issue, I'd be closing some rads to see if heat is forced round parts of system and make sure zonevalve is fitted and working correctly, did a plumber do all your work or was it yourself , ?

 

[SimonG]

Pump

 

[summat]

Pump

Might not be the end of the world - bought a pump-only unit from grundfoss that is supposed to be compatible with the earlier one, but couldn't the old one didn't fall apart as it should have. Meant I ended up buying a complete pump assy, so with this being only 6 months old it should be easy to swap out the pump body without any plumbing work (and with the new isolating valves, with very little water loss).

I would say the pump feels/sounds okay, but it would explain a sudden loss of function.

 

[GE Sonny]

I agree with Kris . 100% sounds like a circulation issues. Did you use a unit to flush the system if so, was flush chemicals / desludger used .Microbore can be flushed but can create more issues if not careful.
I would try closing the upstairs circuit .making sure the 3 port valve is open, and try again . Providing it's gravity and not sealed .Jump in the loft and check the quality of the water in the small tank (F&E) if its dirty and slushy, I would imagine your system is too

 

[SimonG]

Is it a ups2 pump. Is the light on? Is it pulsing? Spinning up for a fraction of a second every 10 seconds or so?

 

[summat]

@GE Sonny: Norstrum Proflush, with a desludger in the system a few days before hand (from memory). Pretty sure 3 port is working (alternating between HW and CH I can feel the appropriate outlet getting hot). F&E is reasonably clean. expansion pipe is hot at the cylinder, but cold in the loft by the F&E tank. Tank contents stone cold. I'm intrigued... "I would imagine your system is too...." what?

@SimonG: UPS2 - I did have it on II (then tried on III). Now that I've read a bit online turned it down to I, but will also try the proportional pressure settings. It is spinning constantly.

@kris: Problem is all the radiator balance valves are seized after 20 years, so isolating individual rads is not an easy option (I'll do it, but not when I get home at 8pm from work... Fan heaters and immersion until the weekend it would seem).

I appreciate the replies.

 

[kris]

Hi summat,, I think you've kinda answered your own question with saying the valves are seized possibly, let us know how u get on , cheers