Some advice please on DHW overheating problem.

[bulltaco]

Hi there. Firsly I'm 75, asthmatic and have heart problems so have been lying very low during lockdown.
The system is an oil fired Grant Vortex Eco boiler, pressurised system, Horstmann CentaurPlus C27 programmer and an immersion heater.
Just after lockdown began, the boiler tripped and I reset it. A few days later with DHW and CH both on, I found the system had overheated and was losing water from the overflow and I discovered that it was the DHW system at fault. During lockdown I've been managing fine with the CH working and immersion working but am careful not to leave the immersion on for more than 2 hours or it overheats and the tank overflows.
Now that lockdown in Scotland is easing and trades are working again I'll get it seen too but am wondering if it's likely to be an outside and/or inside job as I've had no-one in the house for nearly 6 months and I'm still a bit wary!!. My question really is whether or not this sounds like it will need stuff checking inside the house.

 

[sircerebus666]

Outside job

You will need someone gas Safe registered as they will need to remove the case to test / replace components and will also need to test the boiler is safe when the casing is put back on

 

[Madrab]

oil fired Grant Vortex Eco boiler

You will need someone gas Safe registered

 

[ianmcd]

Probably the Immersion thermostat has given up, a cheap item to replace , forget anything that @sircerebus666 , has said you dont need to be Gas safe registered to work on an oil boiler

 

[bulltaco]

ianmcd. Thanks Ian, first thing I did was put a new thermostat in. In fact I borrowed a second one to try with the same result!. I can live with that at the moment, it's the overheating DHW from the boiler that is the real problem. I'll phone the plumber on Monday although, as I say, I'm not too keen in having anyone indoors just yet with this Covid crap.
PS "Gas safe".

 

[oilhead]

Problem is likely to be with a failed expansion vessel if losing water from the 'overflow'. This in turn causes circulation problems and the boiler overheats.

 

[bulltaco]

oilhead. Thanks, I'd rather guessed that the PRV was blowing off , so it's an inside the house job right enough. Thanks again.

 

[ianmcd]

immersion on for more than 2 hours or it overheats and the tank overflows.

Thanks, I'd rather guessed that the PRV was blowing off

so which is it ? is the tank over flowing (open vent system ) or is your pressure releif valve operating ? (sealed system) if you have a sealed sytem you will have a system pressure guage, is it going up to near the 3 bar level ?

 

[ericmark]

Problem is likely to be with a failed expansion vessel if losing water from the 'overflow'. This in turn causes circulation problems and the boiler overheats.

Think likely spot on, as a immersion heater thermostat and central heating boiler thermostat are unlikely to fail at the same time.

Or the ball cock is allowing too much water into header tank if open vented.

 

[bulltaco]

Thanks ericmark. That was my suspicion too."Think likely spot on, as a immersion heater thermostat and central heating boiler thermostat are unlikely to fail at the same time."
My first post did say "pressurised system" which I imagined also meant "sealed system".
So the answer to my real question is that the job requires access into the house, which gives me some concern due to the Covid situation.
Thank you to all who have helped, it's a great site. I made huge use of lots of help during 10 years of rebuilding and extending this house for our retirement. I retired at age 70 but sadly 2 days after moving in my wife dropped dead with a massive heart attack.

 

[ianmcd]

Sorry I was confused by your post, as you said the over flow was running which means you have an open vented system, but if you have a sealed system most probably the expansion vessel needing serviced, if you are worried about Covid , make arrangements with the attending engineer to come in and carry out the job while you remain in a different part of the home and leave cleaning products and ask him/her to spray anywhere they work, they will be wearing gloves and masks anyway, we do this many times a day

 

[bulltaco]

Ianmcd Thanks, that sounds good to me!!

 

[ianmcd]

Ianmcd Thanks, that sounds good to me!!

But dont call it an overflow, you dont have an overflow, you have a PRV (pressure releif valve ) they are absolutely not the same thing

 

[bulltaco]

Just an update on my problem. Oilhead mentioned "failed expansion vessel" and, after genning up on the subject, I discovered that there was no air pressure in the EV and by tapping it, it was obvious it was full of water. It was a simple job to drain and take off the EV, pump out the water and repressurise to 3bar. Glad I didn't have to get anyone in the house as our wee village now has several Covid cases after someone came from Glasgow to visit a friend here. Thanks again to all (especially oilhead) for their responses on the forum.

 

[ianmcd]

Just an update on my problem. Oilhead mentioned "failed expansion vessel" and, after genning up on the subject, I discovered that there was no air pressure in the EV and by tapping it, it was obvious it was full of water. It was a simple job to drain and take off the EV, pump out the water and repressurise to 3bar. Glad I didn't have to get anyone in the house as our wee village now has several Covid cases after someone came from Glasgow to visit a friend here. Thanks again to all (especially oilhead) for their responses on the forum.

are you sure that 3 bar was the correct charge pressure ? that is usually for an unvented HW Cylinder not a boiler, usually 0.8 Bar for system expansion vessels, what colour is the vessel ?