Water pressure & Morco water heater

[David Mutch]

Hi all. In the last week or so, my Morco D61-B has started refusing to fire up unless the temperature control is set to max. This is coupled with a noticeable drop in flow from hot taps, shower, etc. Flow from cold taps seems normal.

 

I suspected a scaled up heat exchanger, so I removed and de-scaled this. There doesn't seem to be any restriction here, however, and on re-fitting, the problem persisted.

 

I then took apart the water control assembly, cleaned it, and checked all parts moved freely. Still no improvement.

 

I then considered that there may be a blockage after the heater, so disconnected the outlet and ran water into a bucket from the bottom of the heater. This time, the burners lit perfectly. When I reconnected the outlet to the plumbing, the problem resumed.

 

This would appear to indicate a blockage after the heater. However, two separate pipes T off after the heater, and there is no blockage in the pipework that feeds these, yet the restricted flow affects appliances supplied by both pipes, and it would seem rather coincidental that there should be a similar blockage in both pipes.

 

I am now wondering whether, despite apparently decent flow in the cold taps, my pump pressure might be low, such that it can provide sufficient pressure to get the burner going when nothing is attached to the heater, but not when appliances are plumbed in for some reason.

 

Is this a possibility? Does anyone have any other suggestions?

 

Thanks

 

David

[Guest]

It's years since I had a Morco, but is there a filter in the pipework somewhere? I have a distant memory of a gauze filter?

[David Mutch]

It's years since I had a Morco, but is there a filter in the pipework somewhere? I have a distant memory of a gauze filter?

 

Hi Catweasel. Yes, there is a filter at the inlet, but no blockage there, I'm afraid. Sorry, forgot to mention this in my post. Thanks though!

[bizzard]

Check the spouts of your taps, especially if you have the smaller caravan type. Often there are tiny filters stuffed up the spouts, on domestic size too. If so dig em out. The shower rose could also be bunged up with limescale.

[David Mutch]

Check the spouts of your taps, especially if you have the smaller caravan type. Often there are tiny filters stuffed up the spouts, on domestic size too. If so dig em out. The shower rose could also be bunged up with limescale.

 

Thanks Bizzard. I'll give that a try, but two blocked taps and a blocked shower all happening at once seems like even more of an unlikely coincidence than two blocked pipes to me. Easier to check/fix, though!

[David Mutch]

Check the spouts of your taps, especially if you have the smaller caravan type. Often there are tiny filters stuffed up the spouts, on domestic size too. If so dig em out. The shower rose could also be bunged up with limescale.

 

Well I'll be darned, you were spot on. I'm sorry I doubted you! Seems something must have dislodged some limescale somewhere in the system and bunged up all me orifices at once. Gert chunks in everything. Cleaned out now and all is well. Thank you ever so much Mr. Bizzard, sir!

[blackrose]

So because gas water heaters are water pressure dependent, was this a case where pressure was restricted by a downstream blockage rather than anything upstream like a loss of accumulator pressure? Interesting. I'd naturally be looking upstream for the cause.

 

I guess it's easy enough to diagnose a blocked tap as the problem by opening a second hot tap? If the heater comes on when the second tap is opened then you know the pressure restriction is downstream of the heater. Would that work?

Edited December 10, 2016 by blackrose

[ditchcrawler]

So because gas water heaters are water pressure dependent, was this a case where pressure was restricted by a downstream blockage rather than anything upstream like a loss of accumulator pressure? Interesting. I'd naturally be looking upstream for the cause.

 

I guess it's easy enough to diagnose a blocked tap as the problem by opening a second hot tap? If the heater comes on when the second tap is opened then you know the pressure restriction is downstream of the heater. Would that work?

Loss of accumulator pressure will not restrict water flow so you can take that one out of the equation.

[BEngo]

So because gas water heaters are water pressure dependent, was this a case where pressure was restricted by a downstream blockage rather than anything upstream like a loss of accumulator pressure? Interesting. I'd naturally be looking upstream for the cause.

 

I guess it's easy enough to diagnose a blocked tap as the problem by opening a second hot tap? If the heater comes on when the second tap is opened then you know the pressure restriction is downstream of the heater. Would that work?

Instant water heaters are dependent on flow, rather than pressure, though they measure flow by looking at pressure drop. A downstream restriction limits the flow and the water heater diaphragm sees that there is insufficient pressure drop and shuts off the gas.

 

If the incoming water pressure is raised the flow rate increases despite the downstream restriction and the water heater sees enough pressure drop to fire up. Once the initial surge has happened and the watet pump is delivering running pressure rather than cut-out pressure the flow rate falls and the gas goes off. If the pump is left to run then it will usually get up to cit-off pressure and so the gas comes back on. Depending on how restricted the outlet is, the cycle can happen quite quickly or relatively slowly.

 

N

[Guest]

 

Well I'll be darned, you were spot on. I'm sorry I doubted you! Seems something must have dislodged some limescale somewhere in the system and bunged up all me orifices at once. Gert chunks in everything. Cleaned out now and all is well. Thank you ever so much Mr. Bizzard, sir!

A terrible thing to happen

Glad you are sorted; Bizz always has solutions to problems such as bunged up orifices

[alan_fincher]

I was discussing a similar issue about a Morco not staying fully fired up with someone the other day, (albeit that they have the balanced flue model, rather than the open flued type). They reckoned they had completely solved the problem by going for a pump that delivers a higher throughput, (though not necessarily a higher pressure at the pump).

 

In their case I think they had gone from one of the Parmax 2.9 models to a Parmax 4.0 model, and from memory the number broadly relates to gallons per minute, (not sure if UK or US gallons though!), so seem to have replaced by a model that increases flow by in excess of another 38 percent, or so.

 

I have an issue like this with our (nearly new) Morco on very long pipe runs, so I'm interested if anybody else has succeeded, (or failed!) to fix it by substituting a pump that can shift more water.

[blackrose]

Loss of accumulator pressure will not restrict water flow so you can take that one out of the equation.

If the incoming water pressure is raised the flow rate increases

[bizzard]

I've always found that instantaneous gas hot water heaters don't run smoothly with accumulators either because of the slight variations in pressure every few seconds as the pumps pressure switch cuts in and out. Whether the flow rate is high or low they like the pressure to be stable.

[blackrose]

In their case I think they had gone from one of the Parmax 2.9 models to a Parmax 4.0 model, and from memory the number broadly relates to gallons per minute, (not sure if UK or US gallons though!)

I thought the (first) digit in the parmax model number referred to the minimum recommended number of outlets in the freshwater system that the pump was suitable for.

[RD1]

We have a Paloma Mk V, the shower head has a flow control tap on the head to reduce water usage, but if someone leaves both the hot and cold taps partially open, then when you require hot water at the sink, you get no start up, as the water is equalising pressure across the taps in the shower, so there is not enough flow pressure. So close taps in shower.... sorted.

Clearly not the situation here, but my advice helped a few on other forums.

[alan_fincher]

I thought the (first) digit in the parmax model number referred to the minimum recommended number of outlets in the freshwater system that the pump was suitable for.

 

Well it doesn't stand #true for the Parmax 1.9, which Jabsco describe as "Efficient, high-flow, self-priming pump serving 2 or more outlets".

 

I'm not convinced my explanation is right either, although if the model numbers did relate to US gallons per minute, they seem roughly correct in terms of UK quoted litres per minute.

 

Either way a Parmax 4 can shift a lot more water than a Parmax 2.9, and I have had it suggested this may help, (though not proved it myself).

[BEngo]

 

Loss of accumulator pressure will not restrict water flow so you can take that one out of the equation.

If the incoming water pressure is raised the flow rate increases

 

Both of the statements are true and not incompatible. With a 'flat' accumulator, the water pressure will still rise to the pump cut-out pressure. The rate of rise I would expect to be higher because there will be little or no flow into the accumulator. The pump will then stop. When the pump stops the pressure will start to fall- somewhat faster than if the accumulator is working because there will be little or no flow from the accumulator.

The down stream effect is that the heater sees rapidly varying pressure and will cycle on and off if the mean water flow rate is not enough to keep the heater on.

 

 

 

 

N

[BEngo]

Well it doesn't stand #true for the Parmax 1.9, which Jabsco describe as "Efficient, high-flow, self-priming pump serving 2 or more outlets".

 

I'm not convinced my explanation is right either, although if the model numbers did relate to US gallons per minute, they seem roughly correct in terms of UK quoted litres per minute.

 

Either way a Parmax 4 can shift a lot more water than a Parmax 2.9, and I have had it suggested this may help, (though not proved it myself).

A bigger flow rate pump helps because (assuming the water heater does not pass all the water the pump provides) the mean flow is higher than with a small pump. The heater mean inlet pressure will be thus be higher ( for any fixed setting of the outlets) and that produces a bigger pressure drop across the heater and the diaphragm does not switch off the gas.

 

N

[alan_fincher]

A bigger flow rate pump helps because (assuming the water heater does not pass all the water the pump provides) the mean flow is higher than with a small pump. The heater mean inlet pressure will be thus be higher ( for any fixed setting of the outlets) and that produces a bigger pressure drop across the heater and the diaphragm does not switch off the gas.

 

N

 

What about two pumps in parallel?

 

I ask because "Flamingo" came with two Parmax 2.9 pumps in parallel, but with stop valves so only one is used, and the other is a standby, if the first fails.

 

If I open both taps, and power both, is it likely to work, or will there be problems because both are trying to pump into the same pressurised system?

 

It's probably worth seeing what happens, I guess? (I've never tried).

[BEngo]

Give it a go. The interesting thing may well be the behaviour of the pressire switches. It will be a miracle if they go simultaneously.

Ideally you would only use one switch but I can see no problems if pump A cuts in first followed by the other. Similarly I dont think it will matter which one stops first.

Remember you may need to beef up the wiring and master switch to run two at once.

 

N