75ZT Community

Any ideas please?

I switched on the central heating for the first time in months yesterday, to find that only the bathroom and hall radiators got hot.

Water heating part of the system works fine.

I switched off the central heating but this morning, while the water heater part was running, the bathroom radiator started getting warm with the central heating switched off.

Not being a plumber, I'm confused

Anybody know what's happening please?

Not any kind of expert but I would at least bleed rads as a first option.

During a period of inactivity air can be drawn into c/h system, especially if the w/h part of it is operational. This also happens even when c/h is in full use. The inducted air rises to highest points (tops of rads) and produces an air lock which restricts and eventually totally blocks water flow because it can't go anywhere (the air is at the top of the rad and the in/out ports are at the bottom). When testing operational condition of rads, feel the lower part of them rather than just the top for warmth. With the boiler turned on, the programmer in the 'on' mode and within the programmed time limits, and the room thermostat on 'full' or max temp, bleed the rads starting with the furthest from the boiler ie last in the run. When the key is turned (anti-clockwise), top of the rad in the side where the square valve can be seen, there will be the hiss of air escaping. Continue until spluttering (a cloth on the floor around the valve is a good thing) and then close off. Do not turn too tight, the valve seat won't take too much welly. When all the rads are done, some may not need bleeding, it is safe to take the football-buttoned cardi off.

May also be a jammed pump? If not used for the summer these [ours certainly] jams. May need to start pump manually. Is it a Grundfos type pump with a screw/nut in the centre which you remove to reveal a screwdriver slot which you turn to release pump? Dave

Thanks chaps

I bled the rads as a matter of course. Insignificant amounts of air.

Does the pump operate during the water heating operation? It is a Grundfos pump.

Also wondering why some of the rads would warm up when only water heating was selected.

Hi Paul ours do especially bathroom rad. Pump only operates for heating.
Switch on heating, Put your hand on the pump, can you feel it spinning? If not undo the centre screw, will be big chrome or plastic one. Inside you will see a screwdriver slot for small screwdriver, turn this screw Dave

You might have motorised valves to open and close the hot water and heating circuits. We have this set up and one of the valves is stuck causing the rads on one ciruit to get hot when only the water heating is on.

OK Dave,

I'll give it a go - thanks

Thanks Bernard.

PS Iforgot to mention, put a small bowl under it when you undo as a few drips may come out Dave

Further to what Bernard mentioned, if you do have valves it may be your system uses the pump for HW and CH. However the common problem is when HW is gravity, so during the period the heating is off, the pump is not running and ends up sticking like Dave said. You could find that there is some gravity circulation even with a stuck pump. Are the rads that are working close to being above the boiler, and near the HW tank?

The other possibility not mentioned yet is a stuck ball valve in the header tank in the loft assuming you have one. Had this at my Mum and Dads, and the water level dropped too low to circulate properly.

It all depends on the setup really. Do you know if you have any powered valves? A good clue: do you have the possibilty to have CH on without HW?

OK chaps.

Pump is not rotating. Took the cover off but couldn't see the screwdriver slot because of the water dripping out

Our controller allows us to have either H/W C/H or both so I guess the little metal box close to the pump is the valve(s)?

Sorry gents missed this being at the yorkshire meet
assuming you DONT have a combination boiler and you Do still have a hot water cyl.

You will have a pump on the main flow from the C/H boiler to the hot water cyl. Just after the pump you will have either a single "three port" valve that directs the water to your hot water tank or your heating system. if not you will have two single valves that will open when hot water or heating is requested by the system.

If the water in the tanks in the loft falls too low due to a stuck ballcock, the first thing that will fail is the hot water.

If the pump sticks you may still get hot water due to the water gravitating.

If the three way valve fails to open you can tell. there is a slide lever on the side of the valve. when it is open for heating the lever can be moved from it's rest position across to the otherside with minimal effort. if it takes effort to move this and you can hear it pulling the motor with the lever then it is not opening.

To check the pump. You will see two valves either side of the pump with square shafts, turn these clockwise as if turning a tap off, The grunfos pump has a chrome centre cap, remove the centre cap. A small screwdriver will fit into the end of the shaft to ensure the pump is free. It is a magnetic induction pump, no gears so they are prone to sticking after a period on none use. Once you have spun the impeller with the screwdriver a few times, replace the cap and turn the valves back on then try your heating. a trusty screwdriver between the pump and the ear will show even the untrained if the pump is running.

For the 3 way valve: With the system set to H/W only, pull the manual lever in the side, you should feel resistance on the lever but you will be able pull it across, when you have done this release it and it should return. Next turn off the H/W and the C/H on. wait a few mins for the valve to position itself. then pull on the same lever and you should feel no resistance at all.

If you need a new pump or three way valve let me know, I have access to a couple at trade prices.

Thanks Dave Is the valve lever visible or do I need to remove / open the metal box?

visible on the side

Thanks Dave. I couldn't see it but I'll take the wall panel off and get a closer look

I am assuming the valve is a metal topped brass body honywell valve. the lever is on the side just above one of the pipes usually below where the cable goes in

I'll find it tomorrow Dave.

Paul if the pump is not rotating its stuck! Stick a small screwdriver in and turn it to start it manually Dave

Paul did you get your heating sorted?