Hot water flow problem from Megaflow CL170

[damian]

I've lived in my house since it was built new in 2001. We have a Megaflow CL170 in the airing cupboard which is supplied by the gas boiler in the kitchen. In the last week the hot water flow pressure from the shower (not a power shower) and hot taps has dropped to almost nothing.

I found some instructions on the side of the Megaflow to reset the airgap, so I did that and it returned the hot flow back to normal for about 5 mins and then the pressure drops off again. Once the Megaflow fills again it is back to decent flow but as soon as it empties a bit the pressure drops off.

The cold water inlet valve is fully open and the cold water pressure in the house seems normal but I don't have a way of measuring it. What I have noticed since looking at this is that the cold water combination valve just before the inlet to the Megaflow seems to be making a little bit of noise - no rattling or anything like that, but I have never noticed any noise from it.

Does anyone have any ideas what could be causing the hot water pressure to drop off after a few mins?

 

[justlead1]

Hi. Is there a inline filter on the unit.

 

[damian]

I can't see a separate filter. Could it be contained within the cold water combination valve? The valve has a bit coming out the side about 100mm which could be a filter or is the regulator? I will try and post a photo of it later.

 

[Toddyplumb]

Yes its in the combi valve

 

[damian]

It's never been replaced, I'm guessing it is worth getting the filter replaced? Would this have caused a sudden loss of pressure? I would expected the pressure to reduce over time if the filter was becoming blocked.

Is this a plumber job or are they user serviceable?

 

[Gray0689]

If the cold supply is ok it's not the filter as it would do both hot and cold there must be a problem with the air gap in cylinder

 

[Gray0689]

Ps a cylinder should be serviced every year

 

[damian]

There is a pressure regulator (3 bar) on the main incoming pipe to the property, it is my understanding that this feeds every cold tap in the house.

Then there is a pipe feeding off this up to the airing cupboard where the combi valve is. This feeds the Megaflow incoming flow and also the shower cold feeds direct. The pipes are labelled so I don't think the output of the combi valve feeds anything other than the Megaflow and the shower. I think the rest of the cold taps in the house are fed direct off the main incoming pipe in front of the combi valve. I have posted a couple of pictures so you can see what I am talking about.

What does the Megaflow service involve. Do they just reset the airgap or is there a lot more to it than that?

 

[justlead1]

Hi Damian. I would appear you do not have a balanced supply. So if only the hot supply has been affected? It is likely the problem surrounds the inlet valve assembly. I am not familiar with this one, and it does not appear to have a filter attached. It is however possible that the small orifice with in the assembly are partially blocked and or the pressure deducing valve have malfunctioned. Owing to the risk potential associated with these systems, it is important that changing components is carried out by persons with knowledge and certification of the subject.

 

[damian]

Thanks for the reply. I think you're right that the combi valve assembly has failed in some way. I have just tried running the shower on cold only, then opened the bath tap. After about 2 mins the shower (on cold only) totally stopped, so it seems clear that the output of the combi vale is insufficient to refill the Megaflow and provide a cold flow at the same time.

I have heard these unvented systems are dangerous in the wrong hands so I will call a plumber. Thanks for the advice.

 

[justlead1]

Hi Damian, From the information gained from images and your text. The cold should not be affected by the combination valve. As the system does not look balanced (the cold taken from down stream of pressure reducing valve) It may be as simple as a stock cock turned down or a major leak underground on cold supply pipe.. How is the cold tap on kitchen sink performing?

 

[damian]

The kitchen sink cold tap is fine operating at the normal flow rate. All the cold taps in the house always seem fine. The only cold flow that is affected is that to the shower which taps off after the combi value, all the other cold water outlets are upstream of the combi valve.

 

[BLOD]

The pipe coming out of the reducing valve housing opposite side of the cartridge (top pipe in 2nd photo) is the balanced cold take off.
Are you in a hard water area - I am & have seen many scaled up cylinders giving these symptoms.

blod

 

[damian]

Yes, the balanced cold take off supply the cold inlet to the Megaflow and also the shower cold feed.

It is very hard water around here (Fleet, Hants). Do you reckon it's time for a new combination valve? I hear that they're a bit pricey?

 

[BLOD]

I'm a sones throw away from you and yes the water is very hard here!

If your problem affects the hot water & the cold (balanced) supply to the shower then yes it's probably the prv thats / blocked or failed.
If the cold to the shower is ok and the problem just affects the hot water then
bottom of cylinder is probably blocked with scale.

The filter is on the end of the prv cartridge but if you've never had the cylinder serviced then it's more than likely to be seized in the housing and you could end up having to fork out for a complete combination valve (about £130 ?)
The cartridge alone is about £80.

Blod

 

[damian]

Blod, thanks for the reply. The cold to the shower is low pressure too, so it sounds like new cartridge or valve time as you say.

Next question then... if you're local to the area do you know of anyone nearby that could fix it?

 

[justlead1]

Hi Damian, Blod has probably crack it. Keep us posted on results, please.

 

[damian]

Hi Justlead1, yes will let you know what happens.

 

[BLOD]

I'll be in Hook this week so if you want me to take a look send me a PM to arrange.

Blod.

 

[damian]

Here's an update on this problem. BLOD called round to have a look and replaced the prv which has sorted the problem. The pressure on all the hot waters taps and the shower is now how it used to be again. Now it is fixed I can see we were putting up with very low flow for a long time before it got really bad.

BLOD told me that he regularly has to replace these prv's or the cartridge after a few years - we are in north Hampshire and the water is very hard. Many thanks to all for your help and especially to BLOD for fixing it.

 

[mrlennie]

Great thread good example of a good forum.

 

[Unregistered]

Hi Damian, just wondering if you got this sorted. I have what sounds like a really similar problem, hot water pressure drops off after a few secs, hard water area etc.
Plumber who came to fix something else mentioned possible valve problem - did you replace yours in the end? Grateful for a steer before a fork out for an expensive part.

 

[damian]

Hi, yes this all got sorted, BLOD from here came to fix it. The problem has been fine ever since.

 

[chris watkins]

Just a word of warning Guest - to work on these systems, even your own, you must be competent i.e. hold a Part G / un-vented ticket. This is a requirement by Law under the Building Regulation.
The reason for this is because these systems can be very dangerous if they are not installed / maintained correctly (have a look at some of the clips on Youtube if you want to frighten yourself)

There are a number of pressure reducing valves now to suit different models & pressures, the original designs of these valves are no longer available it is very easy to by & install these incorrectly.

Please employ someone you knows what they are doing, ask to see their ticket, this is not something which you can diy.

Be safe.

 

[Dotty]

Thread closed because unregistered posters annoy me.