Grant Combi -- no hot water

[copat]

We have a 3-yr-old Grant oil-fired combi boiler -- model MPCOMBI9O.

For a while, we could only get hot (ok warm) water if the CH was on. Now, even with CH turned on, we can't get any hot water. The boiler doesn't turn on at all when running the hot water, but it does come on fine for heat.

Any suggestions?

Thanks.

 

[simond]

Diverter valve.

 

[oilman]

If you can work out how to take the microswitch off the diverter valve, measure how far the pin comes out when you tun the hot tap on. Should be 11mm.

 

[copat]

Thanks.

My husband was able to manually trip the diverter valve, so we think it's ok. We think the heat exchanger is probably covered in lime scale. Is there a good way to clean it? We'd like to try to fix it tomorrow, because the water is freezing and taking a shower is torture!

Thanks for any pointers.

 

[oilman]

It's possible that it's the heat exchanger, but unlikely. It may be the blending valve or the diverter valve. You need to check the pin extension to rule out the diverter valve.

How was the valve "manually tripped"?

You said in your original post the boiler does not come on when running hot water. Is the flow from from the tap about what you'd expect?

 

[copat]

Hi Oilman,

Thanks much for the help!

The flow from the hot tap is much reduced from the rate before the problems started. In fact, the rate is down to what I think must be the cold water that is put back in by the blending valve. I think this is the blending valve because it is the valve that mixes some cold water supply back into the supply that has come off the back of the heat exchanger.

When I was looking at the diverter valve last night, I was focused on the electrical side of it, which works fine. I'll have to go pull the thing apart to check the pin extension. Is the pin movement caused by the pressure change in the tap side of the line? I assume this is the case because I need to turn on the hot tap to measure it.

Does the diverter valve control the cold water (DHW supply) flow to the heat exchanger? Or, does it just use the flow to turn on and off the flow of water from the primary to the secondary heat exchanger? I ask this question because I'm trying to figure out if the reduced flow rate from the hot water tap could be caused by the diverter valve or indicates that the heat exchanger is scaled up.

 

[oilman]

The flow from the hot tap is much reduced from the rate before the problems started. In fact, the rate is down to what I think must be the cold water that is put back in by the blending valve. I think this is the blending valve because it is the valve that mixes some cold water supply back into the supply that has come off the back of the heat exchanger.

It could be the blending valve is scaled up.

When I was looking at the diverter valve last night, I was focused on the electrical side of it, which works fine. I'll have to go pull the thing apart to check the pin extension. Is the pin movement caused by the pressure change in the tap side of the line? I assume this is the case because I need to turn on the hot tap to measure it.

Yes

Does the diverter valve control the cold water (DHW supply) flow to the heat exchanger?

No.

Or, does it just use the flow to turn on and off the flow of water from the primary to the secondary heat exchanger?

Yes.

Make sure you have some new fibre washers, 1/2" and 3/4", then remove the heat exchanger and check the flow through the 1/2" pipes.

 

[copat]

Oilman, thanks so much for your help. It helped to pinpoint the problem.

My husband took apart the boiler and found that the heat exchanger was totally and completely filled with lime scale. He cleaned with a descaler for hours and got as much out as he could and then rinsed and rinsed it. Water was getting through it at that point. He also cleaned out some of the surrounding pipes. He put the boiler all back together and we had warmish water until yesterday. Before, it had been completely cold water.

My husband took it apart again and looked over the diverter valve, which seems ok. He can't get the heat exchanger to clean up enough to be usable, so we're going to have to replace it. Where can we find a replacement part? We can't find anywhere on the web with parts for Grant. The number on the top of the heat exchanger is 15EV N3 2102-163-02. I can't find anything searching for it. We need to get one ASAP. Any idea of how to locate one?

Thanks.

 

[oilman]

Part Center will get you one.