Oil Boiler heating water, but radiators lukewarm

[katie279]

Hi all,

Ok, I'm a dimbo on these things, but I want to avoid the usual lazy forum question 'my boiler's broke how do I fix', so I've tried to detail as much as I can below.
My plumber's down with flu at the moment, so it might be next week before he can look and I'd kick myself if it was something stupid.

Here's the situation:
- Hot water is absolutely fine
- Radiators are lukewarm
- Pump seems to be working (can feel it vibrating if I put my hand on it)

Setup:
- Oil-based boiler - Greenstar Heatslave II External 25/32
- Unvented Cylinder - Evocyl AIR (300L)
- Newish radiators (maybe 4 years old)

Any thoughts/tips most welcome - I've read some posts that talk about air blockage, I don't really know how to 'unblock' this if this is a suspect!


As you can see from photos below, radiators are definitely on, just not very hot and heat centred at the top (although this could just be lack of flow)

You can see in photo below, the water coming into the cylinder is red hot and the pump appears fine (where it says 56.3C)

As per below all the pipes at this stage seem to be hot and working fine, it just becomes lukewarm once it goes into the house:

 

[CBW]

Nice thermal images. The pump seems hot, but not much after that, so could be weak/lazy pump, valve failure. Has this only just started happening? Did it work previously ok?

 

[katie279]

Hi, thanks for your reply - it's certainly been noticeable over the last couple of days, might have been longer. I'd guess it's been a gradual decline over last few weeks.

You could be right on the lazy pump, is there any way to test this?

 

[oilhead]

is the diverter valve working properly? That would be my first port of call.

 

[katie279]

Good idea - I've set the motorised valve to manual this morning and will see if this does anything (assume this is the same thing?!)