poor heating from rayburn 355sfw

[cats paws]

Hi.
I recently installed a rayburn 355 multifuel cooker/boiler and I find that my radiators dont get that warm I use good grade
coal but my hot water is very hot. I have a total heating demand of 36,000btu's I think that it may be undrpowered?

 

[Lime]

I have deleted some of this post.
Please see my post further down.

.............
I wouldn't want to run a coal fire at top heat either, too many clinkers.

 

[chuckey]

If your hot water is "hot" and the rads are cool. It follows then that some thing is not allowing the rads to get hotter and the DHW(domestic hot water) to be cooler. That "thing" could be the two thermostats, an underated pump, a faulty zone valve. . . The big clue is does your rayburn fire continuosly when the house is too cold with the rads getting warmer, but not hot. This would show that the Rayburn is putting all its heat into the rads, but its not enough and indicates that the burner is under rated. If however, the burner cycles on/off while the house is cold, then it shows that the water is not removing the heat fast enough from the boiler, which is cycling on its own thermostat. So the pump might not be working, blockage in pipe, zoning valve stuck. Some of these "fail safe", by opening the DHW port fully and partially closing the rad port. they are not particularly reliable, but normally have an external pointer/or mark to show which position they are in. 36k Bthus is not a very big boiler, like for a two/three bedroom terrace house, but this depends on the level of insulation of the property.
Frank

 

[Lime]

I have obviously taken duff information off the internet as the first webpage I viewed gave the total heat output of this rayburn as 12,000 BThU for the central heating not including the hot water demand.
My first post was based on this and now appears to be wrong.
I will alter it accordingly.

This appears to be the true output
355 SFW - 55,000BTU (9-10 Radiators)

In theory if the demand is only 36,000BThU this range should be able to supply it.
However this link
http://www.rayburn-web.co.uk/raytech/dhw3.htm
talks about cooking making a difference to it's output so perhaps the figure of 55,000BThU is not quite what it seems.

the more cooking is carried out, then the more hot water is generated. With average cooking use, approximately 450 litres (100 gallons) of domestic hot water would be created over a 24 hour period. If the cooker spends longer periods idling, then the hot water production is proportionally reduced, unless of course, a hotter fire is maintained for obtaining central heating. This is assuming that the control damper on the 345W and 355SFW models is set to the cooking position with the firebricks in their appropriate place.

Given the rayburn is correctly fired, all the plumbing correctly installed and the heat setting correct the heating system should be working ok.
However as the hot water is hot but the radiators not then it suggests either a plumbing problem or a setting problem.
There are helpful diagrams etc on the link.

 

[Penners]

cats paws

There are some sensible observations above, but without more information we're all rather operating on guesswork.

You say that you have just installed the Rayburn, but you don't describe the heating/DHW system. Is it a conventional indirect system? Is it perhaps an old gravity system, without a pump on the primary? If the primary is pumped, is there a diverter (zoning) valve that is controlled by a contact thermostat on the cylinder? Is there a roomstat - if so, in which room? Are there thermostatic valves on the radiators?

We need lots more information, please.

 

[cats paws]

Hi. further to your replies regarding my low heat output of my rayburn 355sfw which is only 9weeks old (from new), its run on a gravity feed system 10 out of 11 rads are thermostatic trv's allthough the upper rads get hotter than lower I have tried turning down rads upstairs to push heat down. Although its very good on fuel consumption around 1-2 bags per wk, but will burn wood also.

 

[Lime]

I've seen lots of central heating systems that operate as a gravity fed system when the pump is switched off.
The result is a big waste of heat upstairs.
A simple way to prevent this loss is to fit one or two electromechanical valves to shut off the central heating when the pump is off.
I assume there is a master thermostat that controls the pump?
Relying on thermostatic valves alone is not a good idea.

Also sometimes in poorly designed systems there can be a circulation from downstairs radiators (if hot) to the upstairs too quite independent of the boiler or pump.

Splitting the living-rooms and the bedrooms so that they are on separate thermostatic controlled systems is more economic too.

 

[Penners]

I agree with Lime that relying only on TRV's alone is not a good plan. You also need to be able to concentrate all of your boiler's output on central heating when this is appropriate.

Assuming you have a conventional indirect system (which you don't mention) I think you would see a substantial improvement in the controllability of your heating if you fitted a pump to the primary circuit, with a Y-plan motorised valve activated by a contact thermostat on the cylinder. So once your DHW needs are satisfied, the motorised valve can allocate all the heat in the primary circuit to the rads.

The rads then need to be balanced on the lock-shield valves and the TRV's appropriately set.