Hot Water Tank (heated by OFCH) Only Luke Warm

tm2204

Hi, was wondering is somebody could advise.

My heating system is simple. It's OFCH, F&E tank in loft, Hot water cylinder in hotpress heated by either an immersion heater or indirectly through a coil by the OFCH. No zones, no valves, when heating is on it heats the radiators & the hot water. Normally when i've had my heating on for 2 1/2 to 3 hours it heats a full tank of hot water and it's roasting

Past few days I've noticed my hot water is warm/hot but not hot enough to shower even after the heating has been on for 4+ hours. Have had to run the immersion for a short while to 'boost' the heat before showering. Have never had to do this before.

Had a look in the hotpress and noticed the OFCH feed pipe to the hot water tank is roasting but the return pipe from the tank is stone cold. I don't know if this is normal (doesn't seem right) as have never checked it before. Could I have some kind of airlock in the heating coil in the tank? Why would his suddenly happen?

All the hot taps do run but not as hot as normal.

Any ideas/suggestions?

John.G

A few simple checks first.

Check water level normal in F&E tank.

Check for balancing valve on cylinder return, this normally a gate valve with a red wheel, open it fully (if not already) then shut it fully, approx 4 to 5 full turns, then fully reopen it, if return then gets hot reclose it and open it 3/4 to 1 full turn.

possibly air lock, if no air vent near cylinder you could loosen the compression fitting at the tank coil entry and pull back the pipe a touch to release any air, do likewise at the return at the tank.

Hopefully not, but could also be a holed cylinder coil which is now water logged from the CWST, the bottom of this tank is normally on the same level as the F&E tank but its water level is higher so there should be a slight make up into this (CWST) with no draw off, either cold or hot. If the two levels are equal or a slight overflow from the F&E tank then also indication of holed coil. If the F&E tank is located above the CWST (like mine) then F&E tank will continually make up and the hot (and cold bathroom sink) water may be slightly discoloured.

tm2204

John.G wrote: »

A few simple checks first.

Check water level normal in F&E tank.

Check for balancing valve on cylinder return, this normally a gate valve with a red wheel, open it fully (if not already) then shut it fully, approx 4 to 5 full turns, then fully reopen it, if return then gets hot reclose it and open it 3/4 to 1 full turn.

possibly air lock, if no air vent near cylinder you could loosen the compression fitting at the tank coil entry and pull back the pipe a touch to release any air, do likewise at the return at the tank.

Hopefully not, but could also be a holed cylinder coil which is now water logged from the CWST, the bottom of this tank is normally on the same level as the F&E tank but its water level is higher so there should be a slight make up into this (CWST) with no draw off, either cold or hot. If the two levels are equal or a slight overflow from the F&E tank then also indication of holed coil. If the F&E tank is located above the CWST (like mine) then F&E tank will continually make up and the hot (and cold bathroom sink) water may be slightly discoloured.

Firstly... since I posted this the water in the cylinder is not being heated at all now. Originally it was heating it partially but now it's stone cold.

F&E tank normal water level and working correctly.

No balancing valve.

I'm almost sure this is an airlock although I don't understand how it's happened. Boiler has been heating the hot water cylinder for years now without any issues and this has just happened overnight.

I did what you suggested and loosened the compression fittings at both the flow & return (not at same time) at the tank and, yes, I could hear and see air & bubbles escaping before a flow of water. Tightened them back up again and still no hot water. There doesn't appear to be any trapped air anywhere else in the system... all the rads are piping hot and I haven't had to bleed any. BTW should this be done with the boiler & pump off or running?

Should I drain down the heating system completely and refill? I'll be doing this anyway to fit a MagnaClean filter and a Spirovent Rv2 Deaerator. Alternatively I was firstly going to try shutting off all the rads and letting all the flow run through just the heating coil in the hot water tank... would this "push through" the trapped air as I obv haven't cleared it all?

Don't think it's a holed cylinder coil. Water from my hot taps, although cold, is clean and not discolored.

Thanks.

John.G

Suggest complete drain down then remove the return pipe from the HW cyl coil to make absolutely sure that the coil isn't holed, if it is, water will keep coming out fed from the cylinder contents, even though you have carried out tests re by last paragraph above, then maybe remove flow connection and simply blow through the coil with a bit of plastic pipe to ensure clear. Refill system very slowly.

tm2204

John.G wrote: »

Suggest complete drain down then remove the return pipe from the HW cyl coil to make absolutely sure that the coil isn't holed, if it is, water will keep coming out fed from the cylinder contents, even though you have carried out tests re by last paragraph above, then maybe remove flow connection and simply blow through the coil with a bit of plastic pipe to ensure clear. Refill system very slowly.

Thanks John, I'll give that a try.

When you say refill slowly do you mean restrict the feed to the F&E tank?

John.G

Yes.

tm2204

While I have the system drained down... should I install a bottle automatic air vent on the flow pipe to the cylinder just before it enters the cylinder?

I've seen this done on lots of systems (my mums included) and was wondering if this is good practice to help stop any air locks?

John.G

Yes again, a good idea, also suggest just getting a manual type (which I think are available) as the normal AAV (automatic air vent) tend to get blocked.

tm2204

Cheers John for the advice... all sorted now

Drained down the system... water was pretty horrible :eek: Installed the automatic air vent (had it bought already) beside the cylinder flow. Filled her back up adding chemical cleanser which I'll leave in the system for a couple of weeks before draining down again, flushing once or twice, then final fill and add chemical inhibitor

The HWC is heating up again like normal so problem sorted and now I have the addition of the automatic air vent hopefully this will keep this from happening again.

I'm planning to add a Spirovent Rv2 and a MagnaClean to my system once I have it flushed and ready to refill and inhibit.

John.G

Glad to hear you are sorted.

I'd say you are getting air ingress in your system, possibly for years, to cause this build up of sludge or more unlikely, a small system leak.

I would suggest having a look at the vent and cold feed arrangement before you do anything else and post a picture if you can.
My own open vented system with some rads > 40 years old, has a combined vent and cold feed and there are no air vents anywhere in the system, it was installed like this from new in 1972.
There is another system as well, where, from the boiler flow pipe, you have vent, cold feed then the circ pump with the vent and cold feed no more than 150MM apart. IMO the combined vent and cold feed is the better of the two as it is high up in the system and will not get choked.