No hot water on old floor standing boiler.

[finchy01]

Hi all. I have an old floor standing o/f boiler which isn't giving hot water. I'm wanting to go back to basics on this one as I've tried the 'normal things'!

pumped heating, Gravity dhw. There is a room stat for heating but no stat for hw both are controlled by very old programmer. When I put dhw water only on and switch it to constant I get a hot flow pipe to cylinder but nothing coming out.

i don't think its air in the coil as there is a lovely upward run but to the vent pipe. I've cracked the nut on the flow at cylinder and just got water. Tried bleeding towel rad on circuit, nuts water. Tried pulling through with a hose on the return at the boiler and had my wet vac on the vent sucking any air back.

suggestions would be awesome as I'm beginning to scratch my head and don't really want to take the cylinder out to check for blockages as I believe God put it in in his younger days!!!!

 

[Ermintrude]

Is there a thermo valve on the gravity might have scaled up. Did it work before? Any work done on system before issues?

 

[Best]

Cracking the nut open on the flow at cylinder & getting water proves nothing - even the coil blocked you will get water from the flow pipe & vice versa.
Make sure the flow & return to the cylinder have constant rise & fall. Check the f&e tank is filling into system if you drain a little water from somewhere. If all those check out, then there is a blockage at coil or pipes. Did you try a strong magnet on the pipes to see if any magnetite?

 

[finchy01]

Thanks for the replies guys. It was in fact a slight blockage in the coil. I managed to suck it out and give it a bit a blast through. Nothing major but they are replacing the system in the new year so didn't want to spend too much now.

 

[jtsplumbing]

Old school system, we used to remove boiler stat and boil out air locks, scary mind if you've never done it, buts that's one for us older plumbers.