Oil boiler not heating hot water but most radiators are fine

[dr_bogenbroom]

This is partly a DIY question in that I’d like to try and pinpoint the issue before reaching out to a professional.

We have an old open vented oil heating system, with 2 tanks in the loft. There’s no thermostat and you can’t heat the water in the hot water tank without also having the central heating/radiators on other than the immersion - so it’s basically all or nothing. The hot water tank and the radiator (both in the upstairs bathroom) are stone cold - the other upstairs radiators are fine and so are the downstairs radiators although a couple are a lot hotter than usual.

We also have a back boiler behind the coal fire with its own pump but this is also failing to give any heat to the bathroom radiator and hot water tank

Any ideas what the possible cause of this fault is?

I’m leaning towards there being a blockage of some sort. Because of the age of this system and the fact you can’t have hot water and central heating working independently I don’t think this is a case of a faulty diverter valve as I don’t think it has one, there nothing next to the hot water tank other than pipes.

Thanks

 

[Exedon]

Is there actually water in the small tank in loft?

 

[fourtytwo]

This doesn't make sense, I had what I believe was a similar system, the hot water cylinder being a gravity system and the central heating circuit driven by a pump so if the pump was off but boiler on no hot radiators but plenty of hot water. How else would you get hot water only in the summer.
Perhaps when someone added the back boiler and pump to the coal fire they messed up the original gravity circuit ?
I assume you have just moved into this house and inherited the heating system with no knowledge of it's history ?

 

[dr_bogenbroom]

Is there actually water in the small tank in loft?

Yes there is

This doesn't make sense, I had what I believe was a similar system, the hot water cylinder being a gravity system and the central heating circuit driven by a pump so if the pump was off but boiler on no hot radiators but plenty of hot water. How else would you get hot water only in the summer.
Perhaps when someone added the back boiler and pump to the coal fire they messed up the original gravity circuit ?
I assume you have just moved into this house and inherited the heating system with no knowledge of it's history ?

This is my in laws house where I’m staying at the moment - they’ve been here 35 years and never encountered this issue. You definitely can only have hot water with the heating on as well, unless you use the immersion. We have 2 tanks in the loft, one for cold water and the other I presume is an expansion tank? My knowledge on heating systems is pretty limited.

 

[Exedon]

I take it you have tried to.let air out of non working radiator ?
It may be a airlock but a blocked cold feed a definite possibility.
I wouldn't be using the back boiler until problem is sorted.

 

[dr_bogenbroom]

Not tried letting air out yet but we can try that.

I think the cold feed to the hot water tank is fine as the water still runs out of the hot taps fine, just cold. I can hear the cold tank in the loft filling up when I run the hot tap as well.

 

[Exedon]

It's the cold feed to heating system from the small tank that would be the problem.

 

[dr_bogenbroom]

It's the cold feed to heating system from the small tank that would be the problem.

Ah ok - so the big cold tank doesn’t feed the central heating, it’s the smaller one that does this?

 

[Exedon]

Ah ok - so the big cold tank doesn’t feed the central heating, it’s the smaller one that does this?

Correct that's why I asked about water level in it.

 

[dr_bogenbroom]

For anyone interested we’ve just had a heating engineer round and it turns out there was little to no water in the upstairs radiators (and also I assume the hot water tank coil). They’ve fed water back into the system but what concerns me is where that water that was missing went… If it happens again we’ll need it pressure tested.