Worcester Heatslave 20/25 oil boiler expansion vessel

[Avocet]

The 12 litre expansion vessel in our Worcester Heatslave 20/25 oil boiler has failed. It's a cylindrical one, on a bracket, just above the burner assembly. Unfortunately, they seem to be obsolete. However, a number of places list a replacement, which is rectangular, also 12 litres.

I bought one online and was dismayed to find that it's too big to fit! It's simply too tall to go in the cabinet. Even with the bottom resting on the burner, it's about 20mm too tall and the top would hit the underside of the programmer.

Does anyone have any suggestions, please? I could fit it on the OUTSIDE of the boiler casing, and drill a hole through the side of the casing for the pipe, but that's far from ideal - and possibly illegal?

 

[oilhead]

An external vessel can be fitted to the system. It does not need to be fitted to the case or connected direct to the boiler. You can leave the existing one in situ, or plug the connection, and connect an external one to the return pipework as close to the boiler as practical.

 

[Avocet]

Thanks for that. Currently, my towel rail seems to be acting as an expansion vessel! I can't really think of anywhere else in the system I could fit it, without it looking quite obtrusive. Pop-riveting a bracket to the outside of the boiler casing and hanging it on that, and poking a hole through the casing for the pipe, would be the simplest and most convenient solution for me, if that's not contravening some regulation or other!

 

[oilhead]

Not against any regs, I was thinking of the cosmetics.

 

[ianmcd]

How do you know it has failed and doesnt just need re-Charging PROPERLY ?

 

[BoilerBob]

Yup let the pressure out of the boiler then pump vessel up to 1 bar then pump up the boiler to 1 bar see how it goes. Bob

 

[Avocet]

How do you know it has failed and doesnt just need re-Charging PROPERLY ?

The system would build up pressure fairly rapidly from cold, and then the safety valve would open and it would squirt a bit of water out. On cooling, I'd get air in the towel rail. If I leave it for about a week, the top two bars of the towel rail are cold when the heating is all up to temperature, but at least the blow-off valve doesn't operate!

Also, when I poke the schrader valve on the existing expansion vessel (which has been on for at least 10 years, I'd guess), I get black yukky water squirting out of it.

 

[Avocet]

Not against any regs, I was thinking of the cosmetics.

OK, that's handy to know. Cosmetically, the boiler is in a utility room under a worktop, so the expansion vessel hanging on the outside of it won't look TOO awful. This all happened when I re-decorated my bathroom and took the radiator off to tile behind it. I had to drain the system down to do that, and when I refilled it, this problem started. I did use some central heating cleaner prior to draining it. Not sure if that might have affected anything? It was in the system for a few weeks.

 

[ianmcd]

The system would build up pressure fairly rapidly from cold, and then the safety valve would open and it would squirt a bit of water out. On cooling, I'd get air in the towel rail. If I leave it for about a week, the top two bars of the towel rail are cold when the heating is all up to temperature, but at least the blow-off valve doesn't operate!

Also, when I poke the schrader valve on the existing expansion vessel (which has been on for at least 10 years, I'd guess), I get black yukky water squirting out of it.

Many posts on here about recharging expansion vessels, do it properly, you MUST leave a drain point open when doing it, or it wont work, dont skip steps do it properly , it should be done every year at the service but very few are done

 

[Avocet]

Many posts on here about recharging expansion vessels, do it properly, you MUST leave a drain point open when doing it, or it wont work, dont skip steps do it properly , it should be done every year at the service but very few are done

Gosh! I've seen plenty of people come out and service it and I'm pretty certain NONE has ever touched the expansion vessel!

I take it that the water coming out of the Schrader valve is a pretty certain indication that it's dead though?

 

[ianmcd]

Gosh! I've seen plenty of people come out and service it and I'm pretty certain NONE has ever touched the expansion vessel!

I take it that the water coming out of the Schrader valve is a pretty certain indication that it's dead though?

Nope not at all only way to check is to pressurise it properly

 

[oilhead]

I've had arguments with my OFTEC inspector about this during my assessments. I refused to release the PRV as they often don't seal again, and it is possible to assess any overfull unit with experience. Operating the boiler to test it gives a good indication of how the vessel operates.
If the customer has no problems, then presenting him with a failed PRV on top of service costs is not a good place to be.

 

[Terrywookfit]

It's not unusual to find vessels FULL of water. But drained they will recharge.
Easiest way is to remove them and apply pressure via shraedder valve.

 

[ianmcd]

It's not unusual to find vessels FULL of water. But drained they will recharge.
Easiest way is to remove them and apply pressure via shraedder valve.

The only problem doing tis is , a blocked communication hose or pipe will give the same symptoms and the only way to ensure they are not blocked is to do it with the vessel connected and make sure the water from the vessel is expelled

 

[Avocet]

It's not unusual to find vessels FULL of water. But drained they will recharge.
Easiest way is to remove them and apply pressure via shraedder valve.

That's interesting? I assumed that there was a "rubber ball" inside the vessel, with a Schrader valve attached to it (like a bike inner tube, all in one piece), so the only possible way you could get water out of the Schrader valve would be if the "ball" was punctured somewhere. The existing expansion vessel is welded, so there's no possibility of taking it apart to inspect the "ball".