Boiler/Central Heating Question

RastaManBob · 2 Dec 2010 at 21:54

Hi,

I've noticed a number of threads regarding boilers and home central heating over the past few days, most likely due to the cold weather currently being experienced! Now it's my turn to ask the experts...

I am living in a rented flat which has a combi boiler. It has always been fine for the hot water but until this week I'd never used the central heating.

This week I started using the central heating and am not convinced that it is working quite as it should do. I am not necessarily interested in *how* to fix any problems (unless it really is trivial) rather I'd just like to ensure everything is as it should be... As the property is reasonably new I am sure the landlady could have any repair done under warranty so I am positive it'd be in her interests, as well as mine, that we get any fault fixed... If indeed there is a fault! My concern is asking her to arrange for somebody to come and look only to find nothing wrong!

So, at the moment I have set the temp on the thermostat to 25 degrees c. For the first few minutes everything is fine and the radiators warm up. After a while the noise the boiler makes is different and the burner light is flashing (the manual denotes this to be the boiler is firing up) however it stays in this state for a good five minutes or so before the light goes solid. It is hard to tell if during this time the radiators are getting cooler due their retained heat.

Anyway this pattern appears to keep repeating, hence after having the heating on for approximately four hours it has still yet to reach the target temperature. For this reason I do not think the constant on/off is to do with the thermostat switching after the temperature is reached. Indeed, there is never a moment without the boiler continuing away... The only difference is whether the burner light is solid (and presumably everything is working) or flashing (and in this state I am convinced something is wrong).

Also, when turning the central heating off the device contains to sit in the state with the led flashing. Eventually it will turn off. Alternatively if I use hot water, after stopping the tap the boiler also turns off.

I am sorry that I am unable to explain this better but essentially it seems as though the boiler does not stay "on" for very long before the burner light begins to flash and which point it appears to stay in this state. Very unusual considering if I run the hot water without the central heating on then the burner light flashes for a short time before turning solid and getting hot water... I cannot understand the lengthy flashing stage for central heating.

If anybody has experience, the particular boiler installed is an "Ideal Isar HE35".

Any comments regarding whether what I have described to be correct operation would be really very useful! If you need any further details, or points clarifying please ask. I'd really like to try and determine if everything is working as it should be, or not!

Thanks.

PS. Other threads have mentioned checking that the pressure is correct. I have noticed that when using no central heating or hot water the pressure is at approximately ~0.8 bar. This fluctuates when turned on but settles at around ~1.5 bar. The manual for the boiler states that the "Minimum Domestic Hot Water Inlet Pressure" (is this the value I am interested in?) is 0.5 bar, so I assume ~0.8 bar is fine?

PPS. I've also found this but again not really sure if it is relevant or what it denotes:
Safety valve setting: 3.0 bar. Vessel charge pressure: 0.5 to 0.75 bar. System pre-charge pressure: None | 1.0 bar.

colzboppo · 2 Dec 2010 at 22:26

Ugh. Only thing i'd suggest you do not being a plumber is either top up the pressure on the system (its already fine), or key air out of the radiators.. apart from that.. no idea.. sounds like you need a plumber to have a look at it...?

St0rmer66 · 2 Dec 2010 at 23:10

Don't worry, you're not the first person to ask me this...

There is NOTHING wrong

.

The flashing light on an Isar just means that the flow temperature (water in the pipes) is up to temperature but the thermostat (external control) is still calling for heat. The boiler will switch the burner off but keep the pump running until the flow temperature drops a bit then fires back up again. If you want the flow temperature (and therefore the temperature of the radiators) to be hotter then turn the dial on the front of the boiler (next to the little pic of a radiator) up higher. The Min setting is 30degC, the Max is 82degC (or there abouts). If you run the tap then it will fire up almost instantly as cold water comes into the boiler and triggers a demand, it'll keep on firing for around 5-10 seconds after you switch the tap off to heat the small amount of water in the boiler that's still cold (this boiler keeps it warm inside the boiler at all times, it is never truly "off"). If you still hear the pump running after the demand has stopped (i.e. you switch the heating off or stop running the tap) this again is normal... it will just keep circulating the water around the boiler to dissipate the heat instead of just suddenly stopping and then having massive hot spots around the heat exchanger.

As for your thermostat being at 25... you will never heat the house to that hot in Winter, maybe you would if you put the heating on during the middle of Summer

. 21-22 is plenty for most people, lowering it for better economy. The thing with central heating if you're unfamiliar with it is.. don't pay attention to what the boiler is doing, as long as you're warm enough

. Set the thermostat/timer and then just let it do it's thing until you want to turn it off. Just think about it... you're saying the radiators are hot 'because of their retained heat' but instead of just enjoying the warmth they provide you're wondering why there's a light flashing instead?!

.

Any other questions feel free to ask, I'm very familiar with that boiler (not necessarily for good reasons I'm afraid!).

DBT85 · 3 Dec 2010 at 08:46

stat at 25! sits at 20 in our place and more than comfortable.

chimaera · 3 Dec 2010 at 09:05

Todge said:
stat at 25! sits at 20 in our place and more than comfortable.

Depends on a lot of factors, my thermo is in the hallway which is generally quite warm compared to the rest of the house so the temp needs to be at about 23c in order for the other rooms to hit 20c, plus some radiators are newer so pump out more heat more efficiently than the crappy old ones.

Overall result is that no room in the entire house is at the thermo temperature, it's either too hot or too cold

DBT85 · 3 Dec 2010 at 10:09

chimaera said:
Depends on a lot of factors, my thermo is in the hallway which is generally quite warm compared to the rest of the house so the temp needs to be at about 23c in order for the other rooms to hit 20c, plus some radiators are newer so pump out more heat more efficiently than the crappy old ones.

Overall result is that no room in the entire house is at the thermo temperature, it's either too hot or too cold

you could try some thermostatic valves on the rads. You could set the one in the living areas higher than the one in the hall

RastaManBob · 5 Dec 2010 at 21:46

St0rmer66 said:
Don't worry, you're not the first person to ask me this...

There is NOTHING wrong .

The flashing light on an Isar just means that the flow temperature (water in the pipes) is up to temperature but the thermostat (external control) is still calling for heat. The boiler will switch the burner off but keep the pump running until the flow temperature drops a bit then fires back up again. If you want the flow temperature (and therefore the temperature of the radiators) to be hotter then turn the dial on the front of the boiler (next to the little pic of a radiator) up higher. The Min setting is 30degC, the Max is 82degC (or there abouts). If you run the tap then it will fire up almost instantly as cold water comes into the boiler and triggers a demand, it'll keep on firing for around 5-10 seconds after you switch the tap off to heat the small amount of water in the boiler that's still cold (this boiler keeps it warm inside the boiler at all times, it is never truly "off"). If you still hear the pump running after the demand has stopped (i.e. you switch the heating off or stop running the tap) this again is normal... it will just keep circulating the water around the boiler to dissipate the heat instead of just suddenly stopping and then having massive hot spots around the heat exchanger.

As for your thermostat being at 25... you will never heat the house to that hot in Winter, maybe you would if you put the heating on during the middle of Summer . 21-22 is plenty for most people, lowering it for better economy. The thing with central heating if you're unfamiliar with it is.. don't pay attention to what the boiler is doing, as long as you're warm enough . Set the thermostat/timer and then just let it do it's thing until you want to turn it off. Just think about it... you're saying the radiators are hot 'because of their retained heat' but instead of just enjoying the warmth they provide you're wondering why there's a light flashing instead?! .

Any other questions feel free to ask, I'm very familiar with that boiler (not necessarily for good reasons I'm afraid!).

Thank you for the reply

It certainly put my mind at rest. After your advice regarding the 'stat setting I moved it down to 20. Having never checked the radiators (how stupid...) I moved the thermostatic value setting on them all from 2 to 4. Now the flat gets hotter a great deal quicker and the boiler actually shuts up a lot more (ie, once up to temp, only coming on when the temp drops).

I think my problem was a consequence of having the 'stat too high and the radiator settings too low. I guess this means the boiler was just trying, in vain, to meet the demands set by the 'stat and never quite managed it. This probably also explained why the boiler would occasionally overheat, with the appropriate error code. Either way, now everything is fine. That, in addition to now understand the flashing light, makes me feel a lot more comfortable.

Thank you!