No flow through coil in hot water cylinder All aspects of plumbing questions and answers, help, tips and information

[deckchair]

I have just had a new indirect hot water cylinder fitted but have noticed that there does not seem to be water flowing through the coil, the water on the inward side is hot but the outward side pipes are cold. The plumber said that there was bad sludge in the outward pipes, could this be causing the problems? If not has anyone any ideas?

[ALDA]

Pump running?

If installer knew there is an issue with sludge in pipework, why did the installer not remedy the problem?

These people that dont do a thorough job let the whole industry down!!!

[htg engineer]

Do you get hot water when you open the hot taps ?

ALDA is right - there's no point in fitting a new cylinder or boiler to pipework that is full of sludge. Get the plumber back - ask why it wasn't flushed and get him to flush it and clear airlocks.

This is all part of installing a new cylinder and there should be no extra charge for you to pay.

Find a new plumber for any future work.

[Kenj]

Have you tried venting the pipes to the H/W cylinder?
The problem may be an air lock.
There should be a bleed valve situated just above the upper cylinder pipe. Open this slightly until water escapes.

If this does not work then a build up of sludge may well be the problem.

[Fergusondj]

Sounds like you have pretty much the same problem as I do although I don't have a new cylinder. My cylinder is one floor up from the boiler & pump - when the system is on hot water only the pipes to the cylinder get very hot after the valve but when I check the other end of the pipe at the cylinder its onlt quite warm. I had a guy look at it and he reckons I'm suffering from what he termed a "choke" in the pipework. I've been quoted over £300 to fix it so if there's anything I can do myself I'd obviously like to give it a go.
The central heating systems absolutly fine (microbore) and with the pipework to the cylinder being 22mm could it really be sludge causing the problem?
Is it worh trying a flushing agent added to the system and leaving it to run for a few days before emptying and refilling.

Sorry if I'm hijacking this thread!

[ALDA]

AIR LOCKS AND/OR SLUDGE ARE COMMON TO CIRCULATION PROBLEMS.

"ALWAYS START BY ELIMINATING THE OBVIOUS" I SAY.

FLUSH AND VENT THE SYSTEM.

[Kenj]

Hi Fergusondj, Yes you are hijacking someone else's thread, however !
The probability of a blockage due to sludge in the 22mm pipework to the H/W cylinder, but with the microbore (10mm or less) pipework to the central heating being unaffected is rather remote. So I would not expect flushing the the system to achieve very much.
Heat can radiate along the pipes without any water moving. So with the boiler on and the pump not running, the water in the cylinder feed could get quite hot before the boiler cut out. However, your pump is working fine, otherwise the CH rads would not heat up.
Try venting the H/W cylinder (as in previous post). Another possible cause could be a malfunctioning motorised valve. Many of these have manual overides, try manually opening the valve.
Does your system have one or two motorised valves, and does the hot water heat up ok if CH & HW are selected?

[Fergusondj]

Hi, thanks for your reply. The system has one valve.
If I have the system on hot water only then select CH as well, the valve operates and there is flow to the rads but stlll no flow to the cylinder.
There isn't any facility to vent the cylider that I can see unfortunatly.

The way it's set up all the valve is doing is supplying heat to the CH when open - the circuit to the cylinder is always open.

[Kenj]

It sounds like you have either an air lock, sludge in the pipework, or a blocked motorised valve.
There are many types of 3 way valves. Most, but not all, are open for H/W even when not activated.
There should be some kind of air vent (possibly an automatic one) in the H/W cylinder pipework, whether the system is sealed or open vented.
Unfortunately, you will probably need to start taking things apart to localise this problem. It could be sludge, but this usually accumulates and causes blockages in the lowest pipe runs (ie downstairs radiators), not upstairs cylinders.
You could try a flushing agent, but if it cannot circulate in the cylinder pipework due to a total blockage, it will have little or no effect.
Good luck.

[Fergusondj]

Me again - I've had a really good look at the "design" of my system and having read various articlesd online and at the library I've concluded it's a bit random.

E.G. The cold feed from the expansion tank is teed into the hot water inlet to the cylinder - I can see that at some point it used to be joined to the cylinder outlet but has been altered, why I have no idea.

I don't have a three way valvy btw - that's what I meant by the circuit to the cylinder being always on. The valve only opens when CH is called for otherwise it should circulate round the cylinder but as I've said this is where the problem is - no flow round the cylinder.

All very confusing and as had been said I'm going to have to get my hands dirty.

Wish me luck........

[Fergusondj]

Me again - I've had a really good look at the "design" of my system and having read various articlesd online and at the library I've concluded it's a bit random.

E.G. The cold feed from the expansion tank is tee'd into the hot water inlet to the cylinder - I can see that at some point it used to be joined to the cylinder outlet but has been altered, why I have no idea.

I don't have a three way valve btw - that's what I meant by the circuit to the cylinder being always on. The hot pipe from the boiler is tee'd with one side going to the vavle and the other to the cylinder. The valve only opens when CH is called for otherwise it "should" circulate round the cylinder but as I've said this is where the problem is - no flow round the cylinder.

All very confusing and as had been said I'm going to have to get my hands dirty.

Wish me luck........

[Kenj]

I will indeed wish you luck.
If you are going to drain the systen down and undo pipes to locate your blockage, do not forget to fit a cylinder vent valve while you are at it.

[Dave From Leeds]

Fergusondj, it seems from your description that you have an indirect hot water system. There should be two pipes one directly above the other on one side of the hot water cylinder one near the bottom and the other about halfway up. These are likely to be 22mm copper pipes. The higher one of these should be the hot water feed from the boiler and the lower one the gravity return to the boiler. Have a look to see if there are any other pipes teed off them going upwards, possibly 15mm copper pipes. If so the one from the lower point will be the feed from your central heating top-up tank and the higher one will be the vent to that tank. If you can access this top-up tank, try fitting a hosepipe onto the open end of the vent pipe with the other end attached to a cold tap. Get an assistant to slowly turn on the tap then check for any air coming up through the bottom of the top-up tank. If it does, keep the tap running until the air stops then turn off the tap. If your problem is an airlock in the cylinder heating coil, this should clear it. Be careful not to have the tap turned on too fast or the top-up tank may fill up too quickly for its overflow to cope. This work should be done with your central heating and hot water systems turned off.

[Fergusondj]

Hi Dave - as I said before for some reason the cold feed from the expansion tank used to go into the lower pipe i.e. the return to the boiler but someone has changed this so that it connects to the higher pipe i.e. the flow from the boiler. To be more accurate they've connected it to the vent pipe.

Does anybody know why this would have been done? if I change it back no doubt I'll find out......

If only I could draw you a picture!

[carlb]

Just a quick thought... it is possible that your installer got some debris into the return pipe whilst removing the old cylinder (such as old insulation) if he literally just reconnected the old pipework without alteration. It is quite easily done but luckily also quite easily rectified... Good Luck.