should the F & E tank get warm?

[ricarbo]

Hello folks. Not sure if I've got a problem or not! I've spent weeks updating my heating system in my 2 storey house. Changed the Potterton Kingfisher floor standing boiler for a Glowworm 18 hxi condensing wall mounted boiler, topped up by an f & e tank in the loft. Split the heating into 2 zones, so now there are three zones including domestic hot water, each with a gate valve for balancing. Added TRVs and programmable stats. Finished the pipework on Sundayand am now flushing out the flux etc, prior to finally filling and treating with Sentinel. My question is - the 15 mm feed to the system gets warm/hot, is this ok? The water in the f & e tank gets quite hot too. It seems wasteful of energy and less than ideal as warm water encourages bacteria to grow. The feed is run from the roofspace to the floor of the airing cupboard and then rises 1200mm to fill the system (I thought this arrangement would stop heat getting into the feed pipe). The sequence of connections on the flow side is boiler, 22mm vent, then 70mm to 15mm fill, pump (Grundfoss Alpha+), bypass valve, motorised valves. It occurs to me that the only expansion that actually goes into the so-called expansion pipe (probably better called a vent pipe) is the same few inches that the water level rises in the f & e tank. The rest has to into the feed pipe, so perhaps the way to deal with this is to make the volume of the upward rising part of the feed pipe large enough to contain all the expanded water. That would put the bottom of the loop in the cellar if I had one! Perhaps a better solution would be a vessel installed in the feed pipe line large enough to take the expansion, but i don't know if such a thing is made.
l've got another question, if you can bear it. I change the hot water cylinder to an Albion CF80 quick recovery cylinder some years ago. It has a pocketed thermostat, which I dont think is faulty. If I set this higher than about 30C, the hot water is so hot it is almost dangerous. If I set it a smidge lower, then I get little or no hot water. I think the problem is that the thermostat pocket is actually below the level of the indirect coil, so doesn't pick up the water temperature properly. Maybe i should put a strap-on thermostat on in the usual position? Seems a shame to lose the precision of a pocketed thermosta, though.
My apologies for the length of this enquiry, but I should be eternally grateful fo answers.
Ricarbo (because they say I eat too much carbo- well so does Pavarotti)

 

[ChrisR]

thermostat pocket is actually below the level of the indirect coil, so doesn't pick up the water temperature properly. Maybe i should put a strap-on thermostat on in the usual position? Seems a shame to lose the precision

Use an electronic strap on then if you want precision, like a potterton sensomatic. Your pocketed one hasn't got a hope.

COnnect your feed pipe to the underside of the circuit so it's J shaped. Then you stop convection, but yes the bulk of the expanding hot water does go up the feed not the vent pipe. Only ignorami call the vent the expansion pipe.

 

[chrishutt]

With regard to hot feed tank, this is unlikely to be due to the relatively small volume of expansion. I suspect pumping over from vent pipe - can you check if this is happening, particularly when all zone valves are shut and pump is running on boiler overheat stat (if there is one)?

You could check this by hanging a small receptacle below vent pipe opening to catch a sample of any discharge.

 

[ricarbo]

Thanks Chrishutt, what a quick response! I increased the height of the vent pipe to 600mm above the cold fill level as part of this set up, Glowworm recommend 450mm in the manual, so I went a bit more. I'll try the hanging receptacle trick tonight, but the fill pipe does get warm/hot all the way to the cistern (cooler at the top).
Thanks ChrisR, even quicker! The feed pipe is J shaped, with the upward flowing bit about 1200mm long.
I'll get a Potteron Sensomatic or similar on Saturday. If the manufacturer's set up 'hasn't a hope' and they've made thousands of these things, shouldn't they get it right? I rang them last week and they admitted it can be a problem, just suggested I try adjusting the 'stat. No answer, really. Fit it 3/4 of the way down between the two primary connections, do you think? Or a bit lower to make sure the cylinder is as full as it can be with hot water? By the way, wouldn't the hot water cylinder work better in a fully pumped system if the flow was the lower connection? It's not textbook but would give a higher rate of energy transfer because the temperature difference between the primary flow and the water in the cylinder would be maximised?

 

[ChrisR]

The feed pipe is J shaped, with the upward flowing bit about 1200mm long

I think you misunderstood. J NOT inverted J ? Unless your feed pipe goes 4 foot below the pipe it feeds?

You can expect a litre or two of expanded water from the ch system, so it IS enough to go up into the tank, but once the heating's on the feed pipe cools down unless you have convection.

 

[ricarbo]

Yes ChrisR, the feed pipe goes down 4 foot below the 22mm pipe it feeds before it rises up to the f & e cistern. Is that ok/what we want? The point of connection is on the underside of a horizontal pipe about 70mm away from the vent connection (has to be less than 150mm, I understand) to the left (boiler 3 metres futher away horizontally to the left and 1 to 2 metres lower, in the utility room downstairs) and about 150mm from a slow bend connecting to the suction side of the downward firing pump to the right I put the pump in like this so it doesn't form a collection point for debris.
I think it probably does cool down after the system has stabilised, but won't the temperature be up and down faster than a whore's drawers as the heated volume of water varies with all thes zone valves and TRVs operating at different times?

 

[Beefcake daddy]

Use an electronic strap on

hmmmmm!........

 

[chrishutt]

Did you consider a sealed system? This would eliminate the feed and expansion tank and any problems associated with it. In theory it's a better system because there is no part of system exposed to air.

 

[ricarbo]

Thanks Chris, I hadn't really considered a sealed system before this, because I thought it was just an unnecessary complication, more bits to go wrong etc. Now I'm thinking perhaps it's worth doing! Many thanks.