Central heating - get to temperature then burner hunts

[Mark Doherty]

> My Glowworm Compact 100 boiler does not heat the radiators enough.

> > When the boiler gets up to temperature the burner cuts in for about 5 > > seconds then stops for 1 minute then continually repeats it. Any ideas > If it gets up to temperature then the flame must cut off or the temperature > will continue to rise! > Are you saying that the heat is not being circulated around the radiators?

Yes, albeit they are warm - hot, just not hot enough.

If so perhaps a flow restriction is your problem. The compact has an > internal bypass which if this is all that is clear to flow through will lead > to symptoms such as you describe. > Did this problem start following someone doing some work on the system or is > it a slow developing thing?

The boiler was fitted 2 years ago, I have put up with it cycling for this period as it is generally warm enough and I have been ignoring it, but last week it was colder outside.

> What temperature does the water actually leave the boiler at?

Hotter than the radiators, but the burners are not on for long enough.

> If it is hot, then the boiler may not be at fault. You might have a poorly > > balanced system, a broken zone valve or pump that prevents the hot water > > being pumped through the radiators.

What does 'balanced' mean. (It is fitted to a 3 storey house.) I don't believe I ahve any zone valves. How do you check the pump?

[Set Square]

Is it a combi boiler? [there are several varieties of Compact 100 - some are combis, some are not]

What external controls does your system have? Is there a room thermostat somewhere? What is it set at? Do the radiators have thermostatic valves fitted to them? If so, how are they set?

If not a combi, does the boiler also provide stored hot water? Does that work ok?

[Coherers]

See the Phil Addison's faq on balancing systems at:

I don't believe I ahve any zone valves.

Worth you taking a wider look at the FAQ if you intend to do the work yourself, so you understand the background of what you are doing. They are very good. :-)

[John]

It sounds as though the system was never commissioned correctly when it was installed. Who did the actual installation? Was the boiler connected to an old radiator system or was the whole system new at that time?

As an essential starting point you should read Ed Sirrets faq Once you have read and understood this you are in a position to start looking further. It might be an idea to go round all the radiators and checking how far open the lockshield valves on each radiator are set. Make a note of the settings for future reference so you can at least put them back where they were if neccessary later. Hint close them carefully counting turns and part turns to fully closed. As a starting point once you have made the neccessary record set them to about threequarters of a turn open with the manual or thermostatic valves at the other end of the radiator open or set to high. This will permit you to see if there is now a reasonable flow from the boiler or if there are other causes for the poor circulation. If the boiler was fitted to an old radiator system there is a high probability that there is a significant quantity of sludge blocking the flow and you may need to carry out a flush. For details refer to Google for flushing radiators although the Google files are quite clogged with dross nowadays. Once you have reached this stage ask for more help if you need it

HTH John

[Mark Doherty]

It was a completely new installation (new house)

Did not find this much help on balancing the radiators but

helped alot.

[Mark Doherty]

enough.

Compact 100 System boiler.

thermostat

valves

The boiler is located in the garage. There is a room thermostat in the downstairs hall. All radiators have thermostatic valves (less the towling ones) and are set to their hottest settings. I do not the position of the LSVs.

As an aside, I had a frost stat fitted in the garage but in the winter (and sometimes in the summer) the heating was on all night (the minimum setting was +5). This was confusing to me so I moved it inside the house and set so that it comes on on cold nights, I think it is set to about +8). The boiler already has internal frost protection, so I assumed this was for the external pipes. I don't think (hope not) this is associated!

Is there an easier way to protect the outside pipes (they are lagged)?

The system boiler has a temperature control on the front panel, if I set it to maximum the DHW is too hot to put my hands in the water, hotter than the radiators.

I will attempt to balance the radiators next. Although they all feel the same temperature when they are at their hottest. Does this mean they are balanced?

Under normal circumstances, whilst there is a demand for heat, would you expect the burner to stay on until reaching the demand temperature, or does it reguarly cut out whilst there is a demand thus waiting for the pump to circulate the hot water to cool the boiler down? I presume the boiler will cut out when the water temp is too high.

Thanx Mark

[Set Square]

That still doesn't tell me whether it's a combi. Does it produce 'instant' hot water at the taps, or does it heat up a 30-or-so gallon tankful of hot water for later use?

Bit of a long shot - but is there any chance that the stats are incorrectly wired - so that the frost stat is actually calling the shots and shutting down the heating when it reaches 8 degrees?

They are balanced when the temperature drop across all radiators is equal. You have to be able to run the system continuously for long enough to reach a steady state before you can balance it!

While there is a demand, the pump will run continuously and the boiler may or may not fire continuously. If the radiators can't dump all the heat generated by the boiler, the burner will cut in and out on the boiler stat in order to maintain the required flow temperature.

[John]

SNIP

Great. If you follow the procedure in this then if you are still having problems come back.

[John]

It should - the model compact 100 system boiler is just that, if it was a combi it would be known as the Compact Combi 100 HTH

I had a follow up thought which might be worth checking. There "may" be a bypass somewhere in the system (not the integral bypass within the boiler) which is too far open and thus robbing the flow and return to the radiators of "push" which would strictly limit the flow to them. The excessive bypass return would cause the boiler to think the system was up to temperature and switch the flame off then because of the small amount of recirculating hot water the cool return would rapidly drop the boiler temperature and it would fire again. I still feel that the root of the problem is limited flow to the radiators for whatever reason.