No hot water

[Joe9045]

Hello.
I’m hopingthat some of you nice people can help me.
I have avery simple central heating system. A solid fuel boiler, a circulation pump forthe 7 radiators and the domestic hot water. The system has been working finefor the past 30 years. During this period the system has been drained about 8times, so most of any collected sludge has been flushed out.

Last year,I had to replace a radiator. Fired up the boiler. No hot water. As it was latein the year I left it as I knew I was going to replace 2 radiators this year.
Replacedthese in August. Fired up the boiler. Still no hot water.

Drained thesystem again. Checked the header tank. All clear. I then attached a hose fromgarden tap to the drain cock on the domestic water (return pipe) and forced somewater into the system for a second or two. Re-filled the system very slowly (totry and prevent any air locks). Fired up the boiler and hey presto – Hot waterat last.

All hasbeen fine for 3 weeks, until yesterday, when once again – no hot water.
Today Ikept monitoring the hot water tank. It seems to become luke warm but that’sall.

Does anyonehave any ideas as to what is happening?

Any help,tips or advice would be greatly appreciated.

Joe9045

 

[snowhead]

Is there a vent pipe from the top heating pipe going into the cylinder that then goes up to the header tank?

If not, is there and air bleed (auto or manual) on the top heating pipe going into the cylinder?

If neither you may have to crack the top joint to bleed air.

 

[Old Account]

If you got an air lock you could take a wet vac to suck on the highest outlet the air ... It helped me a lot.

Have you got full pressure of hot and cold or is hot very very low ?

Does your boiler fire when you turn on hot water ?

How is the pressure of hot water downstairs compared to upstairs ?

 

[Joe9045]

Thanks for getting back to me snowhead. This is the first time I have used a forum. Big learning curve. I've tried a couple of times to reply so excuse if you have more then 1 copy of this reply.

Yes there is a vent pipe above the header tank. But no bleed valves anywhere except on radiators.

 

[Joe9045]

Thanks for getting back to me Matchless.plumb

The vac idea seems good. Would I somehow attach it to the vent pipe above the header tank?

I have good pressure all over the house with both hot & cold.

The boiler is solid fuel so there is no firing. Just wait until it all warms up. The radiators work fine. The water from all the taps are only just luke warm.

The pipes from the boiler to the hot water cylinder are warmish.

 

[kris]

Is your hot water pumped or is it work on gravity , ( could be a circulation problem in hot water coil )..
If your system struggles to fill then this suggests air, sludge or badly piped system,
Is there an air point at the coil ( @cylinder)

 

[Joe9045]

Kris, thanks for getting back.
The domestic hot water is just gravity. There is no air vent near the cylinder. The system filled up quite quickly 3 weeks ago and worked fine then all of a sudden it stopped heating again. The rads heat just fine. The whole system has worked great for 30 years, so as you say, could be sludge.
Any fixes apart from an expensive power flush?

 

[stevetheplumber]

have you tried cracking the top union on the primary flow at the cylinder make sure its not air locked

 

[Joe9045]

Thanks for getting back stevetheplumber.

I haven't tried that yet. I take it that "cracking" is just undoing the nut a smidge?
I might look into that over the week-end