Over Flowing boiler Problem

[mcslinger]

I have a Myson Apollo boiler and a conventional heating and Hotwater system.

I have recently replaced the pump (myson 53) with a new one (circulation pumps 53)after it failed but now have the following problem.

When the system is running a small amount of water is coming out of the overflow from the small black plastic tank in the loft. I was told the pump may be set too low so I increased it to the second setting but this only increased the flow of water so I put it back.

I have had it suggested that the thermostats in the boiler might have gone and was wondering if anybody could tell me which. I understand there is one for the return water temperature one for high and one for low.

I am assuming it will be the return as the problem is still there wether the boiler is set to high or low.

If anybody could clear this up for me or has another suggestion then I would be grateful for any information.

[Christian McArdle]

Slowing it down should reduce the flow. However, you might not be able to do so if it is already on the slowest setting, or a slower setting doesn't get everything hot enough. It probably happened when you changed the pump as it was marginal before, but the new pump is just a little more powerful, enough to pump over.

Quite frankly, systems with loft tanks are a complete pain in the arse. You could fiddle around for years with air separators, moving pipework, adjusting valves and pumps etc. Or you could rip it out and replace with a proper sealed pressurised system that simply doesn't have all these problems. There are other advantages too. It is much easier to bleed radiators and flush the system. You get more storage space in the loft. Leaks are less likely, as you can remove pipes from the freezing loft space. Any leaks you do get are much less serious, as there is a limit to the amount of water lost due to the manual fill arrangements.

To make the change, you just need a kit to upgrade, which will include a pressure vessel, pressure relief valve, filling loop and pressure gauge. You install these items, rip out the tank and you're done. It is a relatively simple DIY plumbing job, similar in scope to plumbing in some new taps.

You would need to ensure that your existing system is compatible with sealed operation. This basically means your boiler must have a safety cutout.

See:

(in case of wraps:) exact size you need depends on the size of your system. They have kits from 8 litres to 24 litres. If you know the number and average size of the radiators, you can calculate the minimum size required. Using one that is too big isn't a problem. They vary from 40 to 50 quid including VAT depending on size.

Christian.

[Dave Plowman]

While agreeing that if you actually need the space taken up by the header tank a sealed system may make sense, header tanks worked perfectly well for many years before them. Sometimes the simple way is actually the best.

[Christian McArdle]

I see absolutely no advantages to open systems than these marginal ones:

1. Your boiler might require it.
2. You already have one and don't want to spend 50 quid upgrading.
3. Certain heat bank applications with common circulating water.

The advantages list goes on and on. Header tank systems rarely work well or predictably, which is why sealed operation is now the norm.

Christian.

[Dave Plowman]

Only 50 quid? And how about the reliability of pressure vessels?

I reckon you're much exaggerating the problems with header tanks. And I'd say sealed systems are popular for the same reasons as combis - they are easier to install so make a larger profit for the plumber.

[Michael Chare]

Increasing the pump rate would likely make the problem worse.

One explanation might be a blockage in the system, cause by sludge, or radiator valves (including lockshields) and zone valves not opening enough.

Rasing the maximum height of the overflow pipe might well be a way of solving the problem, so that the vertical distance between the highest point of the overflow pipe and the level of the water in the tank is increased.

Michael Chare

[John Stumbles]

First of all do you mean the overflow (which carries water away from the tank to an open pipe discharging somewhere outside the house where it is|should be visible?

Or do you mean the vent pipe which is roughly like the crook of a walking stick and opens over the tank itself?

From the sysmptoms you describe it sounds to me (and everyone else who's replied to this thread) like the latter. If it is then apart from making sure the top of the walking-stick section is as high as possible above the tank and the water level in the tank when cold is only about 2-3", you should check that the outlet (feed) pipe from the tank and the vent pipe both join the main pipework close together - less than 6" apart.

[mcslinger]

Yes I mean the pipe coming of the small tank to the outside of my house where it is dripping down the wall.

[Christian McArdle]

That's the parts cost, provided you DIY. I reckon it would take me about 2 hours of my time in addition to affix a sealed system kit and cap off the old pipes. This includes drilling a hole through the wall for the pressure relief. The kit simply requires you to insert a T at convenient points in the CH circuit and rising main and attach using compression joints.

Christian.

[Dave Plowman]

Then that's got nothing to do with the pump.

Change the washer in the ball valve.

[Tim (Remove NOSPAM.]

I have a house with header-tank style oil fired CH which has worked for years perfectly fine. We now wish to install 3 new rads in the attic where the header tank is. This was going to involve moving the header tank from its present location almost at floor level up the wall to create enough head to stop pump-over and allow the new rads (300mm installed low as poss) to work.

Had never heard about sealed pressure system you mention. Would there be any problems with fitting such a kit to my system to avoid the bother of moving the header tank like bursting rads or creating leaks where there didnt used to be any...??

There is room in the boiler cupboard, just, probably to install a pressure vessel and there is an outside wall to pop the vent through. What safety cut out does the boiler require? (already has adjustable thermostat as per usual)

Could the pressure vessel be installed in the place of the header tank in the attic or does it have to be nr the boiler?

TIA

Tim..

[Christian McArdle]

I would VERY strongly recommend switching to sealed operation. For loft conversions, it is a no-brainer decision, provided your boiler has the required safety cutouts.

Sometimes, you do get leaks that weren't there before. However, if you do, then it usually indicates that the joint/pipework was on its last legs anyway, so you can be thankful for the warning. Occasionally some radiator unions may need a slight nipping up, but this is rare. If your pipework really can't take 1.5bar, then it is shot. Period.

Yes. It is a popular location for it, as it already has a mains pressure cold water feed, an overflow pipe which can be replaced by a copper pressure relief one, and a connection into the system. The main objection is normally that it is in a loft, where the pressure gauge and refill point are inaccessible. In a loft conversion, this is no longer the case.

When installing, it is advisable to add an additive filling point too, so you can use cheap unconcentrated treatment chemicals. This is simply a short vertical spur of pipe with an isolating valve in it. You pour the chemicals into a funnel at the top before refilling with water.

It just needs a second device to cut the gas if the system starts boiling. This is often a non-adjustable 90-95C manually resetable thermostat next to the main thermostat. If you state the make and model of your boiler, someone here might know if it is already so equiped.

Christian.

[Tim (Remove NOSPAM.]

Fairly sure there isnt any additive in the system at the moment... The only slight complication is that as well as the CH heating the hot water cylinder- an Aga also does so via thermo-syphon. Am not quite sure how both heat sources are plumbed into the cylinder coil, will investigate...

The system works with two motorised gate valves, as opposed to a mid port valve if this makes any difference...?

In that case, no there isnt a 95 C cut out- surely easy to fit as a clamp on pipe arranghement with normally closed contacts..?

Thanks muchly for the info so far

Tim..

[Christian McArdle]

This can get complicated, unless the Aga has its own coil in the cylinder and doesn't share water with the boiler. If it does share water, you're getting into Dunsley Neutraliser territory. I don't know if you can run one of these (or an Aga/Rayburn) with a sealed system. I can't think of a technical reason why not, but you'd definitely have to check and could well be disappointed. Perhaps someone here already knows.

There are other alternatives, depending on how satisfied you are with your system and how deep your pockets are. You could, for example, replace the cylinder with an indirect heat bank. (DPS would be the specialists in this field). Then, the CH circuit would be conventional indirect through the coil (i.e. Y-Plan/S-Plan). The Aga circuit could remain gravity circulated (or pump assisted) using gravity fed water shared with the heat bank. This would have the advantage of providing oodles of mains pressure hot water to the taps, providing superlative multiple shower performance and good bath performance, assuming your water supply is good. If not, you can still use a header tank (possibly pumped) for the cold water supply, you just don't get the advantages of mains water.

Optionally, you can also run the radiators from the heat bank too. Although not strictly necessary, this would enable the Aga to power the radiators, too. It also provides the opportunity through twin thermostat/high hysterysis controls to allow efficient 100% burns from the oil boiler and gives better performance when little heating is required, as the boiler won't drop off the bottom of its modulating range and cycle frequently. (It will cycle using 100% burn over a long period with varying mark/space ratio, which is much more efficient than cycling over a 2 minute period at minimum modulation).

The main disadvantage is that it is difficult to take advantage of condensing operation very easily (if you have a condensing boiler). However, it will condense under many conditions and will definitely take advantage of the greater heat exchanger efficiency. The gains from the anti cylcing nature of the system will probably outweigh the disadvantages of the higher flow temperatures, although mileage may vary.

Christian.