Oil fired central heating never getting to target temperature.

Korkyb

Hi all

My oil fired central heating system seems to have an issue that I can figure out.

The boiler fires up and heats the radiators but then switches off before reaching the room thermostat target (Hive unit).

It seems to stay off for a while before firing up again (during this time the radiators get very cool).

The room thermostat target is set to 20 but the room temperature goes up and down between just under 17 and occasionally reaches just over 18. (the room temperature seems to fluctuate as the radiators heat up then cool down).

Its a fairly large 130 year old granite house (4 bedrooms upstairs, 4 large rooms downstairs (including the kitchen) with poor insulation (upper floor into the eaves).

The radiators get hot enough & if the boiler didn't cut out I cant see any reason that it wouldn't reach the target temperature.

I've tried having the boiler thermostat set at 65 / 75 / 80 / 90 (bleeding hot) - this makes the radiators hotter / cooler but doesn't seem to make any difference to the room temperature reached or the boiler having a little break.

- All radiators in the house get hot. (12 radiators - 6 upstairs & 6 downstairs).
- all but 1 radiator have thermostatic valves (I've tried opening most of them fully in case they are fighting against the room thermostat ???).
- The pump was new last summer & seems to be circulating the water ok.
- The system was drained / cleaned last summer.

Its an older system (Firebird S 90) with a header tank & the hot water tank heats up whenever the heating is on - it can be set to hot water or heating and hot water (I cant have heating on without the hot water tank heating).

Hope that all makes sense - thanks for any advice.

Talldave

I wonder if it's somehow wired up with hot water thermostat and room thermostat in series, so that as soon as one is satisfied, the boiler goes off. Either that or the boiler is going off for its own reason.  It would be fairly simple to trace the "call for heat" signal from the room thermostat with a mains tester and see what's happening. 

Gerry1

What happens if you turn the room thermostat to maximum?

greyteam1959

The room thermostat temperature is only really a guide temperature.
As suggested turn the thermostat up to maximum & see what happens.

Korkyb

I'll try turning up the thermostat tomorrow morning & see what happens.
Off to kip now (just finished night shift this morning   ).

Korkyb

Set the thermostat to 14 overnight & room temp was 14.

Set it to 30, room temp the usual 17.5.....

Hasbeen

Is the boiler turned up to maximum heat setting?

MWT

Flow rate problem perhaps?

At some point the boiler will hit the maximum allowed temperature and cut out for safety if the flow is insufficient, then restart again once it has cooled down...

Hasbeen

MWT said:

Flow rate problem perhaps?

At some point the boiler will hit the maximum allowed temperature and cut out for safety if the flow is insufficient, then restart again once it has cooled down...

So would increasing pump rate help?

matelodave

Having a shufti at the manual - look at page 16. There appears to a Pump Overheat Thermostat which might be cutting off the boiler prematurely if it's either malfunctioning or something is getting too hot.
It's probably a fixed temperature thermal cut-out with a wide hysteresis so it might be worth checking especially if there's an appreciable delay before it resets after it's been tripped. Has it bee replaced in the correct location after the pump change 

Korkyb

My boiler is now refusing to ignite.

It makes all the right noises & sounds as if its running but the boiler remains stone cold.

- I have half a tank of oil
- I've bled the oil to make sure that there isn't an airlocks.
- Switched off & on again (& tried resetting it).

It sounds as if its running normally but not producing any heat at all.

I'm unsure if this is linked to the other issue or just a coincidence but I have a heating engineer coming out today so will hopefully get it sorted.

It may well be time for a new boiler.... this one was in the property when I moved in 18 years ago & not sure how long it had been installed at that point.

I'll update the thread once I have the engineers pearls of wisdom.