Boiler not heating hot water tank! Any ideas?

[adm1]

Hi There,

First post here, so please be gentle....

Anyway, my house has a Grant Eurotherm oil fired central heating boiler running an open vented system with a single hot water tank and 12 rads.

Recently though, it has started taking an extremely long time to heat the water in the hot water tank for a bath - over 3 hours! And even then, we're not getting the same amount of hot water or the same temperature that used to.

The hot water tanks also has an immersion heater, and that heats the water in about an hour, but obviously the electricity cost is more than the oil.

The boiler itself seems to be fine and was serviced about three months ago, when it had new baffles fitted. It comes on fine on the timeswitch, fires up and sounds like it's heating the water, but a mentioned, it takes forever. If we put it on at 4pm, often there's not enough water for a bath for the kids at 7pm! The tank itself is only about five feet away from the boiler.

Any idea what could be causing this problem and how I can test and then fix it?

Thanks,


Alasdair

 

[glasgowgas]

s plan or y plan?

2 x 2 port motorised valves or 1 x 3 port motorised valve?

 

[adm1]

Ummm....good question (goes off to check....)

Right - there don't appear to be ANY motorised valves at all!

From the right side of the boiler, there are two thick (1"?) pipes that look as if they to and from the hot water cylinder. One at the top and one at the bottom of the boiler.

On the left side of the boiler are two thinner 22mm pipes which I guess are the flow and return for the rads. One of these has the pump fitted in it with cutoff valves either side of the pump.

So my guess from this is the hot water cylinder is gravity fed, whereas the rads are pumped?

 

[glasgowgas]

probable blockage in feed/vent pipe

have a look on the FAQs for solutions

probably going to have to cut out some pipe which is blocked and replace

 

[gigz]

Is there an air vent on the top 1" pipe as it enters the cylinder ? If so open it as it could be an air lock. Also do the 1" pipes get hot ?

 

[adm1]

probable blockage in feed/vent pipe

have a look on the FAQs for solutions

probably going to have to cut out some pipe which is blocked and replace

Thanks - do you mean the feed/vent that goes to and from the expansion tank in the loft? I've got no problem cutting pipe as long as i can find the blockage if there is one.

Would it be worth doing a powerflush on the system in this case?

 

[adm1]

Is there an air vent on the top 1" pipe as it enters the cylinder ? If so open it as it could be an air lock. Also do the 1" pipes get hot ?

I don't know the answer to that as the top of the cylinder is hidden inside a cupboard, but I'll pull it apart and have a look. An airlock would make sense though - I guess the copper pipe itself would conduct heat and eventually heat the cylinder even if the water wasn't flowing....and the pipes do get hot, but not massively so.

It would also be an easy fix! Here's hoping......

 

[JohnD]

I am thinking much more of a blockage or shortage of water.

1) climb into the loft and look at the Feed & Expansion tank. Is it empty? Is there a lot of mud at the bottom? Mark the water level with a bit of tape, or measure the depth and note it.

2) If you bleed the highest radiator in the house, does water squirt out forcefully, or does it slow to a trickle? How high is this rad compared to the cylinder?

3) Find the Drain Cock used for draining the system, and a spanner that will fit it. Don't open it yet.

How old is the system? How often do you have to vent the radiators? Is the water black or brown?

Tell us what you find when you have done that...

 

[glasgowgas]

yep mean the feed/vent pipe that goes to and from the f/e tank

where the feed from the tank meets your system pipework its usually tee`d in. its at this tee it generally chokes up ( as the tank shouldnt be running to fill the system, so it starts clogging up)

if its totally blocked NO powerflush or chemicals will shift it.

again look at the FAQs it will tell you how to find a blockage

if you cut out and replace pipework ( its not too hard ) and you get system back up and running, then you can introduce some de sludging chemicals and finish off with inhibitor

best of luck

 

[adm1]

I am thinking much more of a blockage or shortage of water.

1) climb into the loft and look at the Feed & Expansion tank. Is it empty? Is there a lot of mud at the bottom? Mark the water level with a bit of tape, or measure the depth and note it.

2) If you bleed the highest radiator in the house, does water squirt out forcefully, or does it slow to a trickle? How high is this rad compared to the cylinder?

3) Find the Drain Cock used for draining the system, and a spanner that will fit it. Don't open it yet.

How old is the system? How often do you have to vent the radiators? Is the water black or brown?

Tell us what you find when you have done that...

Okey Dokey ......all done! heres the answers:

1) Expansion tank has approx 4.5 inches of water in it, with maybe a quarter inch of brown muck on the bottom of it. The outlet from the expansion tank appears to be clear, and the thing refills happily when the ball is pressed down.

2) Highest rad bleeds fine - good jet of water out of it, and the water is clear, not black. The bottom of this rad is probably about 4 foot above t he top of the hot water cylinder.

3) Drain cock is near the bottom of the boiler. I have spanners

I actually don't know how old the system itself is, but the boiler is probably 6-8 years or so. I tend to bleed the rads every 3 months or so in the winter, but never in the summer. there was a fair bit of air in there just now, so i bled the lot of them.....

 

[adm1]

yep mean the feed/vent pipe that goes to and from the f/e tank

where the feed from the tank meets your system pipework its usually tee`d in. its at this tee it generally chokes up ( as the tank shouldnt be running to fill the system, so it starts clogging up)

if its totally blocked NO powerflush or chemicals will shift it.

again look at the FAQs it will tell you how to find a blockage

if you cut out and replace pipework ( its not too hard ) and you get system back up and running, then you can introduce some de sludging chemicals and finish off with inhibitor

best of luck

Thanks. So there's 2 pipes from the tank - one I presume is the vent as it's plumbed to just hang over the expansion tank. The other which I presume to be the feed comes out of the bottom of the tank....so i need to trace that to the first "T" point on it - which would be the likely contender....? Presumably a magnet to find a blockage?

 

[JohnD]

from bleeding the radiator position, it sounds less likely you have a blocked F&E pipe (this is good)

Now that you have marked the water level in the F&E tank, tie up the ball float so that it will not refill. Go down to the drain cock and drain out half a bucket of water. Return to the F&E tank. You should find it has dropped by the same amount you drained out.

Untie the ball valve* and it should deliver half a bucket of water, then stop,

please advise if this works,

If so, please post some pics of the pipes, valves and pump around the boiler and the hot cylinder. Describe the distance (horizontal and vertical) between the two.

*p.s. before untying the ball valve, you can if you want bale out the brown mud and sponge it clean. This will do nothing but good, as it will remove sediment that might otherwise flow down into your pipes.

 

[adm1]

from bleeding the radiator position, it sounds less likely you have a blocked F&E pipe (this is good)

Now that you have marked the water level in the F&E tank, tie up the ball float so that it will not refill. Go down to the drain cock and drain out half a bucket of water. Return to the F&E tank. You should find it has dropped by the same amount you drained out.

Untie the ball valve* and it should deliver half a bucket of water, then stop,

please advise if this works,

If so, please post some pics of the pipes, valves and pump around the boiler and the hot cylinder. Describe the distance (horizontal and vertical) between the two.

*p.s. before untying the ball valve, you can if you want bale out the brown mud and sponge it clean. This will do nothing but good, as it will remove sediment that might otherwise flow down into your pipes.

John,

All done....no issues.

I tied up the ball valve, then drained about 10L from the drain cock. Checked the expansion tank and it had emptied down. Untied the ball valve and it fills back to the original level and stops.

Seems the feed works OK.

While I was up there, I traced the feed pipe. It runs into the centre bar of a T. One of the cross ends of the T then dives downstairs. However - the other side of the T bar appears then to run back to the top of the expansion tank as the expansion flow. Is that correct? It's a little difficult to tell as it's a n old house and the pipes go behind timbers, but that's what it looks like.

 

[adm1]

Here's some pics:

Here's the expansion tank

Left hand side of the boiler - 2 22mm pipes coming out. Drain cock is off the bottom one so i guess that's the cold water infill. Also the pump is in this pipe. The slanting bit of 15mm in the picture is just a spare bit of loose pipe - not attached.

Right side of boiler - 2 28mm pipes. These go through the wall into the airing cupboard

Here's the cylinder itself. I haven't disassembled enough of the cupboard yet to see it all, however out of the picture, there is a pipe coming off the top of the cylinder - with no bleed valve, and another one coming off the right hand side pretty high up. Again, no bleed on that either as far as I can see.

The high left hand pipe with the T to 15mm connects to the top right pipe on the boiler. The low left one connects to the bottom right pipe on the boiler. I think. the boiler is about 4 feet to the left of the cylinder, and the base of the cylinder is about 2 feet higher than the top of the boiler.

Hope this helps!

 

[JohnD]

That's good, you have not got a blocked or dry F&E.

I can't see anything odd (I am a householder not a pro but have done these)

looks like you have 28mm gravity feed to cylinder, the 15mm rising from the upper cylinder pipe should go off to the F&E

The Tee you mention would normally have 22mm left side (part of circulation); 15mm upwards (to F&E); 22mm right side circulation continues

the 15mm I see in the boiler pic might be the F&E pipe, in which case there may not be a Tee. If it is in fact 22mm it might be the vent pipe that is bent over the F&E pipe

If the boiler is very old it might have sludge at the bottom, interfering with the gravity flow a gravity HW circulation has very little flow so sludge can build up there (OOI a few weeks ago I converted my old mum's from gravity HW to pumped, and it dislodged a considerable amount of black and brown sediment, even though I had previously given it a chemical clean and fitted a Magnaclean)

Did you get sediment out of the drain cock?

It never hurts to give an old open system a chemical clean, as they usually have a lot of sediment in them. it will only cost £15 for the cleaner and £15 for some new inhibitor. If you can do basic plumbing and can afford £100 you can fit a Magnaclean as well, I guarantee you will be amazed and delighted to see how much black sediment it collects. However I don't know if the problem is caused by Sediment or something else. I normally use X400 but X800 will I understand work OK and only takes a matter of hours rather than weeks.

Let's see if any of the pro's can spot anything else.

p.s. feel both the 28mm pipes between boiler and cylinder and see if they are both too hot to hold.

It looks like you have a gate valve which is to restrict flow to cylinder and stop it taking all the flow (when you have radiators on). If you open it, count the turns from current position to fully open so you can put it back after finishing tinkering.

p.p.s. when you have finished, put thick Climaflex lagging on all those hot pipes, they are pouring money away in wasted heat