Water not getting fully hot 12 January at 6:07PM in In my home (includes DIY) MoneySaving 12 replies 311 views

PuxtatawneyJont

Hi I was hoping to get some clues as to why my hot water is only getting luke warm in the cylinder. It used to get hot after about 30 minutes, now after 1hr 30 mins it's only luke warm even though the pipe to the cylinder is getting hot. I have an indirect cylinder fed from a tank in the loft. The heating works fine and the 3 way motorised valve seems to be working as it should, i.e the heating and HW systems only kick in when called for. I recently balanced the radiators and everything has been absolutely fine for about a month. I wanted to balance the HW coil but I'm not sure where the valve for this is located. There is one on a pipe that connects near the bottom of the 3 way valve which I've adjusted in and out but it makes no difference. There is also a flat headed screw on the inlet or outlet pipe on the tank (on the top pipe halfway up the cylinder). I wondered if there might be a blockage or an airlock? Many thanks in advance.

nofoollikeold

1. Pictures?
2. It's possible the valve you have altered (near bottom of 3 way valve) is to balance flow between hot water and heating.  If you have nearly closed it, you won't get so much heat in the cylinder coil.

grumbler

Also, the cylinder thermostat is worth checking if the 3-way valve is operational.

ThisIsWeird

The pipe to the cylinder is getting hot? This is from the motorised valve to the top (well, middleish) cylinder connection? Is this pipe AS hot as the one feeding the m'valve? And what does the return - bottom pipe - from the cylinder feel like?

Motorised valves can become sloppy and sticky, I think more likely than a blockage is a 22mm pipe.

The cylinder stat works ok? Clicks at the correct temp?

PuxtatawneyJont

nofoollikeold said:

1. Pictures?
2. It's possible the valve you have altered (near bottom of 3 way valve) is to balance flow between hot water and heating.  If you have nearly closed it, you won't get so much heat in the cylinder coil.

I've had the valve half open and fully open.It's the one in the first pic

grumbler said:

Also, the cylinder thermostat is worth checking if the 3-way valve is operational.

It was new 18 months ago but I'll look into testing it.

Mutton_Geoff

That valve is not to balance the hot water system, there is no such thing as there is only one heat emitter. It is a system bypass to allow water circulation through the boiler to keep the boiler below its high energy cut-out temperature (around 85C), as this would result in the boiler overheating and the boiler locking out.

This forum can be dangerous with the advice posted 

The fault is likely to be the cylinder stat. Has it stopped calling for heat when the water temp is still lukewarm? Has the temp control on it been knocked/adjusted? It's tied to the cylinder by that elastic band. Pull back the insulation to check it's located & set properly.

The install is a bit scrappy too. Looks like the plumber chucked all the parts onto the floor and joined them up where they fell.

FreeBear

You need to move those cables out of the way so that they are not in contact with the hot pipes.

ThisIsWeird

PuxtatawneyJont said:

nofoollikeold said:

1. Pictures?
2. It's possible the valve you have altered (near bottom of 3 way valve) is to balance flow between hot water and heating.  If you have nearly closed it, you won't get so much heat in the cylinder coil.

I've had the valve half open and fully open.It's the one in the first pic

grumbler said:

Also, the cylinder thermostat is worth checking if the 3-way valve is operational.

It was new 18 months ago but I'll look into testing it.

The motorised valve in the first pic will have the boiler's hot flow coming up to its bottom connection. It is then diverted to CH, DHW, or BOTH. As you clearly know :-)

In that first pic, the valve pipe coming out towards us supplies the DHW - the cylinder (check it has an 'A' embossed on the brass body near the pipe connection). The one at the back ('B') goes to the CH circuit. (If I got this the right way around.)

The valve you ringed in the first pic would appear to be a manual by-pass valve. This allows a controlled amount of the flow from the boiler to return to the boiler's return without it going through the rest of the circuit, ie CH or DHW. The flow can 'bypass' the circuit, and just head straight back to the boiler.

Then I get confused. The bypass appears to be coming from the flow pipe to the 3-porter - ie the 'AB' connection underneath - which would be correct, but I cannot see where the other end of it goes - could you take some more photos to confirm, please?

Bypass valves are used to ensure there is always enough flow getting out and back to the boiler so it doesn't 'cycle', ie produce hot water it cannot get rid of, which would make it trip the overheat stat on and off. Imagine a CH system with TRVs - when all are shut (rooms warm enough), there will be very little flow getting out of the boiler, so it would be constantly going off and on, perhaps even overheating the water. The bypass allows it to always have some water flow. Manual bypass valves are crude, tho', and 'auto' make more sense - they only open if needed, and send all the flow around the circuit at other times.

In your circuit, I cannot tell where the bypass is connected to at its far end - photos, please. In general, tho', the more 'open' it is, the less flow that goes to the circuit, and the more goes straight back to the boiler. Clearly it's daft to have too much going back to the boiler, because the actual circuits would be starved of hot flow, and the boiler would be getting a hot return, and thinking it's done its job - and shut off the burner.

You shouldn't really be playing with bypass valves, but - if you do - a rule is to always mark where it is before messin', so you can always put it back where it was before.

The ringed thingy in the second pic looks like an air vent - I presume that pipe is high up, possibly the highest point in the circuit? It needs a radiator key, and open it a turn should release any collected air. Worth a try - only one turn open max - and with the boiler OFF.

I'm guessing your circuit is 'vented' - you have a small F&E tank in the loft, and no pressure gauge?

I agree with others - that plumbing is just awful. There is limited space in there, yes, but that's even more reason to get it neat. I hope the slope the pump is on is in an acceptable direction - photo?

Make and model of boiler?

FreeBear

ThisIsWeird said: I hope the slope the pump is on is in an acceptable direction

Not a recommended orientation. The pump motor should be horizontal, not vertical or at an angle. But with the way the pipework is laid out, probably difficult to reposition the pump.

PuxtatawneyJont

The fault is likely to be the cylinder stat. Has it stopped calling for heat when the water temp is still lukewarm? Has the temp control on it been knocked/adjusted? It's tied to the cylinder by that elastic band. Pull back the insulation to check it's located & set properly.

We checked the cyl stat last night with multimeter, it seems to be working as it should. It's been set to 60. It never seems to stop calling for heat as the boiler is always on (with the heating turned off).

ThisIsWeird said:

The motorised valve in the first pic will have the boiler's hot flow coming up to its bottom connection. It is then diverted to CH, DHW, or BOTH. As you clearly know :-)

In that first pic, the valve pipe coming out towards us supplies the DHW - the cylinder (check it has an 'A' embossed on the brass body near the pipe connection). The one at the back ('B') goes to the CH circuit. (If I got this the right way around.)

The valve you ringed in the first pic would appear to be a manual by-pass valve. This allows a controlled amount of the flow from the boiler to return to the boiler's return without it going through the rest of the circuit, ie CH or DHW. The flow can 'bypass' the circuit, and just head straight back to the boiler.

Then I get confused. The bypass appears to be coming from the flow pipe to the 3-porter - ie the 'AB' connection underneath - which would be correct, but I cannot see where the other end of it goes - could you take some more photos to confirm, please?

Bypass valves are used to ensure there is always enough flow getting out and back to the boiler so it doesn't 'cycle', ie produce hot water it cannot get rid of, which would make it trip the overheat stat on and off. Imagine a CH system with TRVs - when all are shut (rooms warm enough), there will be very little flow getting out of the boiler, so it would be constantly going off and on, perhaps even overheating the water. The bypass allows it to always have some water flow. Manual bypass valves are crude, tho', and 'auto' make more sense - they only open if needed, and send all the flow around the circuit at other times.

In your circuit, I cannot tell where the bypass is connected to at its far end - photos, please. In general, tho', the more 'open' it is, the less flow that goes to the circuit, and the more goes straight back to the boiler. Clearly it's daft to have too much going back to the boiler, because the actual circuits would be starved of hot flow, and the boiler would be getting a hot return, and thinking it's done its job - and shut off the burner.

You shouldn't really be playing with bypass valves, but - if you do - a rule is to always mark where it is before messin', so you can always put it back where it was before.

The ringed thingy in the second pic looks like an air vent - I presume that pipe is high up, possibly the highest point in the circuit? It needs a radiator key, and open it a turn should release any collected air. Worth a try - only one turn open max - and with the boiler OFF.

I'm guessing your circuit is 'vented' - you have a small F&E tank in the loft, and no pressure gauge?

I agree with others - that plumbing is just awful. There is limited space in there, yes, but that's even more reason to get it neat. I hope the slope the pump is on is in an acceptable direction - photo?

Make and model of boiler?

Thank you for your detailed response. The motorised valve is oriented with A going to CH and B going to HW.

Pic below shows other end of bypass, same valve ringed as previous pic:

I have no idea where the horizontal pipe under the floorboards goes to, sorry.

It seems to me that the more the valve is closed, the hotter the water should get?

As for the ringed thing, it is on the highest pipe. I opened it but didn't hear any air escaping.

I had a plumber in 18 mths ago because I was getting bad kettling from the HW system. He was a total rogue. He put on a new cyl stat (after breaking the old one) and motorised valve (probably my perfectly good old one!) but it didn't make any difference. He then opened up that bypass valve and it cured the problem for a bit. He said my heating system was clogged up and it couldn't be powerflushed because it has 8mm pipes going to the rads, so it therefore needed an entire new, modern system installing.  I've since drained and flushed the system (water was flowing fine through the system from the outset, no sign of any blockages), flushed out the oldest rads, cleaned out the F and E tank, balanced and bled the rads and installed Sentinel X200 and everything's been fine.

I was loathe to chuck out the old boiler because it's been very reliable and efficient, despite it being an Ideal Icos!

ThisIsWeird

If no air out that bleed screw, then likely there's no air. So that's good.

I can't follow the pipe layout on my phone, so need to wait before I'm home to see it on a big screen.

Theoretically, yes - the more the by-pass is closed, the more the hot water is forced through the cylinder loop, so the faster the water is heated up. I have to say, I am struggling to understand the logic of the bypass valve, tho' - why do you want any water going straight back to the boiler, unless it's on the CH circuit which has TRVs that can close off? Never fully understood that.

Have you fitted a magnetic filter to the return to the boiler? If you can, do so. You can add chemicals via it, but you'll also soon know if what the plumber said - you have sludge - is true. AND, you want to catch that sludge if it does exist...