DIY Doctor UK DIY Forums

Hi all - first post, so hope someone can help.

I have an open vented indirect HW & CH system. An Ideal Classic LX boiler and a Grundfos UPS 15-60 pump set on speed 1 of 3.

Sequence of events:- Boiler fires up in morning to heat hot water and CH. Pump runs, rads and hot water start to heat up. loud water rushing noises coming from hot water cylender/boiler. after approx 15 mins very hot water enters F&E tank in loft via the vent pipe, and boiler over temp button pops out. Re setting the trip button restarts system, and until recently would be ok till following morning, however now button pops out again after a short time with associated venting into F&E tank. After some experimenting, problem seems to be associated with only the hot water side of the system, as if I switch the water off on the controller, the CH works fine on its own - if water only, or water and CH, problem returns!

Does anyone have any idea what is going on here?

By the way the whole system is 15yrs old, the boiler is serviced annually, and in recent years the system has had a replacement pump, thermostat, and thermal cut out.

Any help would be greatly appreciated as I am at my wits end with this problem.

Thanks in anticipation

Brighamy.

If its only on DHW operation are you sure its pumping over into the F&E tank? There are probably two tanks up in your roof. The big one which is your CWST and the F&E. Not being rude but it is important to know which.

You may have a blockage where the feed comes down from the F&E and jons the primary circuit. Pumping over into the F&E is to be expected in this case and using a chemical cleaner will usually NOT solve it. The affected pipework need to be cut out and replaced. This would normally occur for DHW only, DHW and CH or CH only.

You may have a perforation in the coil in the cylinder. In this case then I would expect the system to pump over into the CWST and this will definately only occur when DHW is on.

How is the primary circuit piped? It should be boiler, vent, feed, circulating pump.

If circulator speed is too high then it can happen. Whats it set to?

Alternatively you may have a problem with your motorised valve(s). Do you have a single 3 port valve or 2 x zone valves?

Many variables here and we may not be able to fix it remotely so you should perhaps consider getting someone in. Lets find out a bit more about your system first per the above.

Cheers

Hi Rosebery

Thanks for the reply. Yes, it is definatly the small F&E tank. As to how the primary cct is piped, afraid thats way over my pay scale, and I have no idea. Circ pump is set to 1 of 3, and I have a motorised 3 port valve.

Following on from my post yesterday, I have bled the circ system via the pipe with a knurled nut next to the hot water cylender, and increased the circ speed to level 2. I had no problems this morning when everything fired up, but I fear this may be a false dawn as I am treating the symptoms and not the cause.

Best regards

Brighamy.

The reason the reset button keeps activating is due to wear, they are only supposed to be use as a safety feature, constant use will wear them out. There is still a fault with your system. It is possibly a bad installation.

[quote="plumberman666"]The reason the reset button keeps activating is due to wear, they are only supposed to be use as a safety feature, constant use will wear them out. There is still a fault with your system. It is possibly a bad installation.[/quote]

The red button is activating because the boiler is over-heating. I suspect your boiler thermostat is faulty.