Back boilers

green-backer

Does anybody know about back boilers. The type behind a gas fire. Mother in law has such a system and needs rads bleeding. How does the system refill? She doesn’t have any gravity fed system. Hot water cylinder present. Is there likely to be a valve to refill the system behind the gas fire as I can’t see one anywhere else? 

tacpot12

Are you certain she doesn't have a gravity-fed system? Most of the back boilers I've come across were installed with gravity feed for the hot water and pumped central heating, and had a header tank either above the cylinder or in the loft. If it is a sealed heating system, there must be a filling loop somewhere, and probably a pressure guage. 

Have a look to see if there is a Cyltrol valve next to the cylinder. If you Google "cyltrol valve", you find lots of pictures of brass valves with blue knobs on top. If she has a Cyltrol valve, this is more evidence that the system is gravity fed, or at least used to be. Does your mother-in-law remember any work being done on the heating system to fit a room  thermostat? If there is no room thermostat in the house, this is more evidence of a gravity fed system (just based on age alone).

Note that if you have a Cyltrol valve, the cylinder might also be a Primatic type, which means that the water in the heating system can mix with the domestic hot water (although it should not under normal circumstances). This means that corrosion inhibitor should never be added to the heating system. (If the heating system is pressured, the cylinder cannot be a Primatic type). Does your mother -in-law know if the cylinder has ever been replaced? 

Another thing you can try is to actually bleed the radiators. On a gravity fed system, the pressure in the system is quite light, but water will keep coming out forever if you keep the radiator bleed open, and yo may be able to hear the ball !!!!!! in the feed tank letting water into the system to top it up. (Only try this on the highest radiator in the house!) On a pressurised system, the pressure will fall as it isn't being topped up. This should stop the boiler from working, as there should be an interlock, so you may not want to try this when it is cold outside and the heating might be needed soon.

My feeling is that this must be a gravity-fed system, as back boilers can be dangerous when connected to sealed systems as they take a whiel to cool down so they can produce dangers pressures and temperatures until a pressure releif valve and a boiler interlock is provided. This seems unlikely. 

FreeBear

Never had a Cyltrol valve on my old heating system (Baxi Bermuda back boiler & gas front). Did have the twin header tanks in the loft though - Made life so much easier to add corrosion inhibitor to the system and it would automatically refill as the radiators were bled.

green-backer

Ok thanks all. There is a fixed thermostat installed downstairs. I’ve never looked in the loft but my wife and mother are certain there are no tanks. Illl check myself though. I’ll have a look for those valves and report back. The hot water cylinder is original. Will take a pic when I’m over there. 

Section62

green-backer said:

Ok thanks all. There is a fixed thermostat installed downstairs. I’ve never looked in the loft but my wife and mother are certain there are no tanks. Illl check myself though. I’ll have a look for those valves and report back. The hot water cylinder is original. Will take a pic when I’m over there. 

The header (/F+E) tank for a gravity heating system is pretty small - could be easily missed if the loft has other stuff in it.  You'd normally expect it to be more or less directly about the hot water cylinder.  Another clue would be having multiple pipes going up from the airing cupboard to the loft.

green-backer

Section62 said:

green-backer said:

Ok thanks all. There is a fixed thermostat installed downstairs. I’ve never looked in the loft but my wife and mother are certain there are no tanks. Illl check myself though. I’ll have a look for those valves and report back. The hot water cylinder is original. Will take a pic when I’m over there. 

The header (/F+E) tank for a gravity heating system is pretty small - could be easily missed if the loft has other stuff in it.  You'd normally expect it to be more or less directly about the hot water cylinder.  Another clue would be having multiple pipes going up from the airing cupboard to the loft.

Good point about the pipes. Will take a look on Saturday and let u know.