Dual open coal fire backboiler 5 rads, piping hot with Oil but only lukewarm with BB.

T

tommym

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Hi could any one help, i moved into a house about a year ago it has an open coal fire with a back boiler, when the fire is lit it only heats the 5 radiators luke warm, yet when i turn my oil heating on everything is realy hot ?...Thanks, Tommy
 
It may be as simple as cleaning the boiler plate. A lot of back boilers/wrap around boilers become coated with a very heavy slag build up which stops the conduction heat transfer from the coals to the water inside the boiler.
This slag will have to be scraped using a good paint scraper and glove, preferably when there is a good hot fire down.
You may have to check the system to see if there is a non-return valve on the pipework at the oil firing boiler. If this is not in place the back boiler will be heating a cold oil boiler leading to heat loss and short circuiting problems.
Check the heating coils on the hot water cylinder to see if there is a throttling gate valve fitted. These valves can be throttled back allowing more water to circultate to the heating system. Note: This valve should not be fitted to the primary circuit between the back boiler and the hot water cylinder.
If there is pipe thermostat fitted near the back boiler(generally fitted to the flow pipe) check to see if this stat is operating and bringing on the circulating pump. The pump may be very old and not up to circulating water along distances and through radiators.
Depending on the age of the back boiler you may have a problem within the boiler with sludge build up leading to circulating problems.
Hope this helps as this is just a shot in the dark without physically looking at the installation.
If all else fails you may need to get a qualified plumber with expertise in dual heating systems to have a look at the installation and burn coal in the fire!!
 
Thanks Villa 1, I cleaned everything as you said, now rads are hot up stairs, but when i put on the pump everything goes luke warm again,,,,regards Tommy
 
I would not expect a back boiler to have the same output as an oil boiler, The oil boiler is much more capable of heating all of the rads.
 
You must remember that different types of coal work best in different types of appliances .

But in your case , the radiators are losing heat when you turn on the circulating pump .

It sounds like you need to follow ' villa 1 ' advice
 
Is there a non-return valve on the oil heating circuit? If so, it could be seized open and allowing the back boiler to be heating the oil boiler, taking many of the kw from the solid fuel circuit. If not one, fit one on the positive side of the oil boiler circutlating pump.

Also remember that a solid fuel back boiler is probably running at about 40% efficiency so for every kg of fuel that you put into it, 60% of the useful energy within that fuel is going straight up the flue and into the atmosphere. It will never be able to keep up with the energy conversion of an oil boiler. Even an older type can be got up to in the region of 84% efficient. You will also need to be prepared to keep a continous feed of fuel into it to keep the kwh output for the back boiler. Depending on the fuel type, will also be a factor on the output of the boiler.
 
We have a back boiler and oil heating for the last 30 years and there is a significant difference in heating the house with each.

If you want to heat upstairs and down using back boiler and the pump switched on, you will have to keep a pretty big fire in the grate to keep heat in the all rads.

We use the back boiler only in milder weather when we need less heat. The fire has to be going for some time with plenty fuel applied before you can use the pump. Upstairs rads will heat up quickly without the pump and water will be hot but once you have to pump the water around the rads that's when you get much lower heat output. I would use the oil to start off during cold spells and if you have the fire lit, you could then switch off the oil, increase the fuel on the fire and then use the pump. That's the only way in my experience to get full value out of both.
 
What speed are you using on the back boiler pump? If its on "3" try cutting it down to "2" the higher speed is circulating the water too fast through the back boiler. Keep a sharp ear out for boiling (knocking etc).
 
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